Pulsed-based time of flight methods and system

ABSTRACT

A time of flight sensor device is provided that is capable of generating accurate information relating to propagation time of emitted light pulses using a small number of measurements or data captures. By generating pulse time of flight information using a relatively small number of measurement cycles, object distance information can be generated more quickly, resulting in faster sensor response times. Embodiments of the time of flight sensor can also minimize or eliminate the adverse effects of ambient light on time of flight measurement. Moreover, some embodiments execute time of flight measurement techniques that can achieve high measurement precision even when using relatively long light pulses having irregular, non-rectangular shapes.

BACKGROUND

The subject matter disclosed herein relates generally to optical sensordevices, and, more particularly, to sensors that use light based time offlight measurement to generate distance or depth information.

BRIEF DESCRIPTION

The following presents a simplified summary in order to provide a basicunderstanding of some aspects described herein. This summary is not anextensive overview nor is it intended to identify key/critical elementsor to delineate the scope of the various aspects described herein. Itssole purpose is to present some concepts in a simplified form as aprelude to the more detailed description that is presented later.

In one or more embodiments, a time of flight sensor device is provided,comprising an emitter component configured to emit a light pulse at afirst time during a measuring sequence; a photo-sensor componentcomprising a photo-detector, the photo-detector comprising a photodevice configured to generate electrical energy in proportion to aquantity of received light, a first measuring capacitor connected to thephoto device via a first control line switch, a second measuringcapacitor connected to the photo device via a second control lineswitch, and a third measuring capacitor connected to the photo devicevia a third control line switch, wherein the photo-sensor component isconfigured to set a first control signal of the first control lineswitch at a second time during the measuring sequence defined relativeto the first time, and reset the first control signal at a third time,wherein setting the first control signal at the second time andresetting the first control signal at the third time causes a firstportion of the electrical energy proportional to a leading portion of areceived reflected light pulse corresponding to the light pulse emittedby the emitter component to be stored in the first measuring capacitor,and set a second control signal of the second control line switch at thethird time, wherein setting the second control signal at the third timecauses a second portion of the electrical energy proportional to atrailing portion of the received reflected pulse to be stored in thesecond measuring capacitor; and a distance determination componentconfigured to determine a propagation time for the light pulse based ona first measured value of the first portion of the electrical energy, asecond measured value of the second portion of the electrical energy,and a third measured value of a third portion of the electrical energycorresponding to ambient light stored on the third measuring capacitor.

Also, one or more embodiments provide a method for measuring a distanceof an object, comprising generating, by a photo device of aphoto-detector of a time of flight sensor device comprising a processor,electrical energy in proportion to a quantity of light received at thephoto device; emitting, by the time of flight sensor device, a lightpulse at a first time within a measuring sequence; setting, by the timeof flight sensor device at a second time during the measuring sequencedefined relative to the first time, a first control signal of a firstcontrol line switch; resetting, by the time of flight sensor device at athird time, the first control signal, wherein the setting the firstcontrol signal at the second time and the resetting the first controlsignal at the third time causes a first portion of the electrical energyproportional to a leading portion of a received reflected light pulsecorresponding to the light pulse to be stored in a first measuringcapacitor connected to the photo device via the first control lineswitch; setting, by the time of flight sensor device at the third time,a second control signal of a second control line switch, wherein thesetting the second control signal at the third time causes a secondportion of the electrical energy proportional to a trailing portion ofthe received reflected pulse to be stored in a second measuringcapacitor connected to the photo device via the second control lineswitch; and determining, by the time of flight sensor device, apropagation time for the light pulse based on a first measured value ofthe first portion of the electrical energy, a second measured value ofthe second portion of the electrical energy, and a third measured valueof a third portion of the electrical energy corresponding to ambientlight stored on a third measuring capacitor.

Also, according to one or more embodiments, a non-transitorycomputer-readable medium is provided having stored thereon instructionsthat, in response to execution, cause a time of flight sensor device toperform operations, the operations comprising initiating emission of alight pulse at a first time within a measuring sequence; setting, at asecond time during the measuring sequence defined relative to the firsttime, a first control signal of a first control line switch; resetting,at a third time, the first control signal, wherein the setting the firstcontrol signal at the second time and the resetting the first controlsignal at the third time causes a first portion of the electrical energyproportional to a leading portion of a received reflected light pulsecorresponding to the light pulse to be stored in a first measuringcapacitor connected to the photo device via the first control lineswitch; setting, at the third time, a second control signal of a secondcontrol line switch, wherein the setting the second control signal atthe third time causes a second portion of the electrical energyproportional to a trailing portion of the received reflected pulse to bestored in a second measuring capacitor connected to the photo device viathe second control line switch; and determining a propagation time forthe light pulse based on a first measured value of the first portion ofthe electrical energy, a second measured value of the second portion ofthe electrical energy, and a third measured value of a third portion ofthe electrical energy corresponding to ambient light stored on a thirdmeasuring capacitor.

To the accomplishment of the foregoing and related ends, certainillustrative aspects are described herein in connection with thefollowing description and the annexed drawings. These aspects areindicative of various ways which can be practiced, all of which areintended to be covered herein. Other advantages and novel features maybecome apparent from the following detailed description when consideredin conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized block diagram of a TOF sensor illustratingpulsed light time of flight principles.

FIG. 2 is a block diagram of an example TOF sensor device according toone or more embodiments.

FIG. 3 is a diagram of an example architecture for a baselinephoto-detector.

FIG. 4A is a timing diagram illustrating an example timing of events forcapturing a trailing edge portion of a reflected pulse by aphoto-detector.

FIG. 4B is a timing diagram illustrating an example timing of events forcapturing a leading edge portion of a reflected pulse by aphoto-detector.

FIG. 4C is a timing diagram illustrating timings associated with captureof the entirety of a reflected pulse.

FIG. 5 is a timing diagram illustrating a charge capture sequencerepeated over a sequence of multiple pulses.

FIG. 6 is a diagram of an example architecture of a photo-detector for aTOF sensor device that includes two measuring capacitors.

FIG. 7 is a timing diagram illustrating an example measuring sequencethat can be carried out in connection with a two-capacitorphoto-detector.

FIG. 8 is a diagram of an example architecture of a photo-detector for aTOF sensor device that includes three measuring capacitors.

FIG. 9 is a timing diagram illustrating an example measuring sequencethat can be carried out in connection with a photo-detector thatincludes three measuring capacitors.

FIG. 10 is a diagram of an example architecture of a photo-detector thatincludes three measuring capacitors for measuring the leading portion ofa pulse, the trailing portion of a pulse, and ambient light,respectively.

FIG. 11A is an example timing diagram illustrating the signal, receivedlight, and measuring capacitor charge timings for measuring pulseinformation in accordance with a ratio method.

FIG. 11B is a timing chart illustrating TX1 and TX2 switch timings fortwo example measuring sequences that can be combined to extend themeasurable distance of a TOF sensor device.

FIG. 11C is a timing diagram illustrating three measuring sequenceswhereby each sequence has a different pulse width, pulse amplitude, andnumber of pulses.

FIG. 12 is a timing diagram illustrating measurement of four calibrationdata points during a calibration sequence for compensating formismatches in capacitance.

FIG. 13A is an example timing diagram illustrating the signal, receivedlight, and measuring capacitor charge timings for measuring pulseinformation in accordance with a center of mass method.

FIG. 13B is a timing diagram illustrating TX1 and TX2 switch timings fortwo measuring sequences in which the sampling time for the secondsequence is delayed relative to the sampling time for the first sequenceby a duration smaller than the pulse duration.

FIG. 14 is a chart plotting four measured voltages as a function of anemission time of a pulse relative to the start of a measuring sequence.

FIG. 15 is a plot representing a light pulse shape reference.

FIG. 16 is a plot representing normalized reference pulse integrals ofthe reference pulse plot of FIG. 15.

FIG. 17 is a chart that plots normalized reference pulse integral data.

FIG. 18 is a flowchart illustrating general steps of an iterativeprocess for determining a propagation time of a non-rectangular lightpulse.

FIG. 19 is a flowchart of an example methodology for determining adistance of an object or surface corresponding to a pixel of a TOFsensor image.

FIG. 20A is a flowchart of a first part of an example methodology fordetermining a distance of an object or surface corresponding to a pixelof a TOF sensor image using a ratio method.

FIG. 20B is a flowchart of a second part of the example methodology fordetermining the distance of the object or surface corresponding to thepixel of the TOF sensor image using the ratio method.

FIG. 20C is a flowchart of a third part of the example methodology fordetermining the distance of the object or surface corresponding to thepixel of the TOF sensor image using the ratio method.

FIG. 21A is a flowchart of a first part of an example methodology fordetermining a distance of an object or surface corresponding to a pixelof a TOF sensor image using a center of mass method.

FIG. 21B is a flowchart of a second part of the example methodology fordetermining the distance of the object or surface corresponding to thepixel of the TOF sensor image using the center of mass method.

FIG. 21C is a flowchart of a third part of the example methodology fordetermining the distance of the object or surface corresponding to thepixel of the TOF sensor image using the center of mass method.

FIG. 21D is a flowchart of a fourth part of the example methodology fordetermining the distance of the object or surface corresponding to thepixel of the TOF sensor image using the center of mass method.

FIG. 22 is an example computing environment.

FIG. 23 is an example networking environment.

DETAILED DESCRIPTION

The subject disclosure is now described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding thereof. It may be evident, however, that the subjectdisclosure can be practiced without these specific details. In otherinstances, well-known structures and devices are shown in block diagramform in order to facilitate a description thereof.

As used in this application, the terms “component,” “system,”“platform,” “layer,” “controller,” “terminal,” “station,” “node,”“interface” are intended to refer to a computer-related entity or anentity related to, or that is part of, an operational apparatus with oneor more specific functionalities, wherein such entities can be eitherhardware, a combination of hardware and software, software, or softwarein execution. For example, a component can be, but is not limited tobeing, a process running on a processor, a processor, a hard disk drive,multiple storage drives (of optical or magnetic storage medium)including affixed (e.g., screwed or bolted) or removable affixedsolid-state storage drives; an object; an executable; a thread ofexecution; a computer-executable program, and/or a computer. By way ofillustration, both an application running on a server and the server canbe a component. One or more components can reside within a processand/or thread of execution, and a component can be localized on onecomputer and/or distributed between two or more computers. Also,components as described herein can execute from various computerreadable storage media having various data structures stored thereon.The components may communicate via local and/or remote processes such asin accordance with a signal having one or more data packets (e.g., datafrom one component interacting with another component in a local system,distributed system, and/or across a network such as the Internet withother systems via the signal). As another example, a component can be anapparatus with specific functionality provided by mechanical partsoperated by electric or electronic circuitry which is operated by asoftware or a firmware application executed by a processor, wherein theprocessor can be internal or external to the apparatus and executes atleast a part of the software or firmware application. As yet anotherexample, a component can be an apparatus that provides specificfunctionality through electronic components without mechanical parts,the electronic components can include a processor therein to executesoftware or firmware that provides at least in part the functionality ofthe electronic components. As further yet another example, interface(s)can include input/output (I/O) components as well as associatedprocessor, application, or Application Programming Interface (API)components. While the foregoing examples are directed to aspects of acomponent, the exemplified aspects or features also apply to a system,platform, interface, layer, controller, terminal, and the like.

As used herein, the terms “to infer” and “inference” refer generally tothe process of reasoning about or inferring states of the system,environment, and/or user from a set of observations as captured viaevents and/or data. Inference can be employed to identify a specificcontext or action, or can generate a probability distribution overstates, for example. The inference can be probabilistic—that is, thecomputation of a probability distribution over states of interest basedon a consideration of data and events. Inference can also refer totechniques employed for composing higher-level events from a set ofevents and/or data. Such inference results in the construction of newevents or actions from a set of observed events and/or stored eventdata, whether or not the events are correlated in close temporalproximity, and whether the events and data come from one or severalevent and data sources.

In addition, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or.” That is, unless specified otherwise, or clearfrom the context, the phrase “X employs A or B” is intended to mean anyof the natural inclusive permutations. That is, the phrase “X employs Aor B” is satisfied by any of the following instances: X employs A; Xemploys B; or X employs both A and B. In addition, the articles “a” and“an” as used in this application and the appended claims shouldgenerally be construed to mean “one or more” unless specified otherwiseor clear from the context to be directed to a singular form.

Furthermore, the term “set” as employed herein excludes the empty set;e.g., the set with no elements therein. Thus, a “set” in the subjectdisclosure includes one or more elements or entities. As anillustration, a set of controllers includes one or more controllers; aset of data resources includes one or more data resources; etc.Likewise, the term “group” as utilized herein refers to a collection ofone or more entities; e.g., a group of nodes refers to one or morenodes.

Various aspects or features will be presented in terms of systems thatmay include a number of devices, components, modules, and the like. Itis to be understood and appreciated that the various systems may includeadditional devices, components, modules, etc. and/or may not include allof the devices, components, modules etc. discussed in connection withthe figures. A combination of these approaches also can be used.

Time of Flight (TOF) optical sensors—such as photo detectors ormulti-pixel image sensors—are generally used to detect distances ofobjects or surfaces within a viewing range of the sensor. Such sensorscan include, for example, photo detectors that measure and generate asingle distance data point for an object within range of the detector,as well as multi-pixel image sensors comprising an array ofphoto-detectors that are each capable of generating a distance datapoint for a corresponding image pixel.

Some types of TOF sensors that employ pulsed light illumination measurethe elapsed time between emission of a light pulse to the viewing field(or viewing space) and receipt of a reflected light pulse at thesensor's photo-receiver. Since this time-of-flight information is afunction of the distance of the object or surface from the sensor, thesensor is able to leverage the TOF information to determine the distanceof the object or surface point from the sensor.

FIG. 1 is a generalized block diagram of a TOF sensor 112 illustratingpulsed light time of flight principles. In general, the sensingtechnology used by some TOF sensors measures the time taken by a lightpulse to travel from the sensor's illumination light source—representedby emitter 104—to an object 108 or surface within the viewing field andback to the sensor's light photo-detectors, represented by sensor 106.Sensor 106 can be, for example a dedicated multi-pixel CMOSapplication-specific integrated circuit (ASIC) imager that integratesspecialized means for measuring the position in time of received pulses.Distance measurement components 102 measure the distance d to the object108 as

d=(c/2)t  (1)

where c is the speed of light, and t is the measured time of the roundtrip for the pulse from the emitter 104 to the object 108 and back tothe sensor 106.

Emitter 104 of the TOF sensor 112 emits a short pulse 110 into theviewing field. Objects and surfaces within the viewing field, such asobject 108, reflect part of the pulse's radiation back to the TOF sensor112, and the reflected pulse is detected by sensor 106 (e.g., aphoto-detector or a photo-sensor such as a photo-diode). Since the speedof light c is a known constant and the time t elapsed between emissionand reception of the pulse 110 can be measured, the distance measurementcomponents 102 can determine the distance between the object 108 and thesensor by calculating half of the round-trip distance, as given byequation (1) above. Collectively, the distance information obtained forall pixels of the viewing space yields depth map data for the viewingspace. In some implementations, distance measurement components 102 caninclude a timer that measures the arrival time of the received pulserelative to the time at which emitter 104 emitted the pulse. In general,the TOF sensor 112 generates information that is representative of theposition in time of the received pulse.

When radiation of the reflected pulse is incident on the photo-receiversor photo-detectors that make up sensor 106, the incident light isconverted into an electrical output proportional to the intensity of theincident light. The distance measurement components 102 then recover andanalyze the electrical output in order to identify the pulse, therebydetermining that the reflected pulse has been received at the sensor106. Accurate distance measurement using light pulse time delayestimation depends upon reliable recovery and representation of thereflected light pulse and its time related characteristics.

In some implementations, the photo-detectors of sensor 106 accumulateelectrical charges based on the exposure duration of the sensor 106 tothe received light pulse radiation relative to a time reference. Theaccumulated charges translate into a voltage value that is used by thedistance measurement components 102 to recognize the pulse. Once thepulse is identified, the distance measurement components 102 canestimate the time that the reflected pulse was received at the TOFsensor relative to the time that the pulse was emitted, and the distancecan be estimated based on this time using equation (1) (or anotherdistance determination equation or algorithm that defined distance as afunction of light pulse propagation time).

The TOF sensor's photo-detector should be designed to enable accuratemeasurement of information representative of pulse time of flight andpulse amplitude over a large dynamic range. For applications in whichfast response times are essential—e.g. industrial safety applications inwhich the TOF sensor output is used as a safety signal—accurate objectdetection with minimal response times is crucial. TOF detection methodsthat can achieve highly precise detection measurements while relying ona small number of pulse captures and data points are preferable for suchapplications. Such methods must also be able to compensate for (or beinsensitive to) the effects of ambient light. Also, many TOF distancemeasurement techniques rely on pulses having a substantially rectangularshape (e.g., negligible rise and fall times with a reasonably flat andconsistent amplitude), and can lose measurement precision when longpulses of irregular shape are used.

To address these and other issues, one or more embodiments of thepresent disclosure provide a TOF sensor capable of accurately measuringinformation relating to the propagation time of light pulses andcalculating the time of flight to and from an object or surface in theviewing field using a small number of measurements or data captures,thereby maintaining short acquisition and response times. TOF distancemeasurement systems and methods described herein also implementtechniques that minimize or eliminate adverse effects of ambient lighton the TOF measurement, and that can achieve high measurement precisioneven when relatively long light pulses of irregular shape are used.

FIG. 2 is a block diagram of an example TOF sensor device 202 accordingto one or more embodiments of this disclosure. Although FIG. 2 depictscertain functional components as residing on TOF sensor device 202, itis to be appreciated that one or more of the functional componentsillustrated in FIG. 2 may reside on a separate device relative to TOFsensor device 202 in some embodiments. Aspects of the systems,apparatuses, or processes explained in this disclosure can constitutemachine-executable components embodied within machine(s), e.g., embodiedin one or more computer-readable mediums (or media) associated with oneor more machines. Such components, when executed by one or moremachines, e.g., computer(s), computing device(s), automation device(s),virtual machine(s), etc., can cause the machine(s) to perform theoperations described.

TOF sensor device 202 can include an emitter component 204, aphoto-sensor component 206, a distance determination component 208, acalibration component 210, a control output component 212, a userinterface component 214, one or more processors 216, and memory 218. Invarious embodiments, one or more of the emitter component 204,photo-sensor component 206, distance determination component 208,calibration component 210, control output component 212, user interfacecomponent 214, the one or more processors 216, and memory 218 can beelectrically and/or communicatively coupled to one another to performone or more of the functions of the TOF sensor device 202. In someembodiments, one or more of components 204, 206, 208, 210, 212, and 214can comprise software instructions stored on memory 218 and executed byprocessor(s) 216. TOF sensor device 202 may also interact with otherhardware and/or software components not depicted in FIG. 2. For example,processor(s) 216 may interact with one or more external user interfacedevices, such as a keyboard, a mouse, a display monitor, a touchscreen,or other such interface devices. TOF sensor device 202 may also includenetwork communication components and associated networking ports forsending data generated by any of components 204, 206, 208, 210, 212, and214 over a network (either or both of a standard data network or asafety network), or over a backplane.

Emitter component 204 can be configured to control emission of light bythe TOF sensor device 202. TOF sensor device 202 may comprise a laser orlight emitting diode (LED) light source under the control of emittercomponent 204. Emitter component 204 can generate pulsed light emissionsdirected to the viewing field, so that time-of-flight information forthe reflected light pulses can be generated by the TOF sensor device 202(e.g., by the distance determination component 208).

Photo-sensor component 206 can be configured to convert light energyincident on a photo-receiver or photo-detector array to electricalenergy for respective pixels of a viewing space, and selectively controlthe storage of the electrical energy in various electrical storagecomponents (e.g., capacitors) for distance analysis. Distancedetermination component 208 can be configured to determine a propagationtime (time of flight) for emitted light pulses for respective pixels ofthe viewing space based on the stored electrical energy generated by thephoto-sensor component 206, and to further determine a distance value ofan object or surface corresponding to a pixel within the viewing spacebased on the determined propagation time.

The calibration component 210 can be configured to execute a calibrationsequence that measures capacitance mismatches between measuringcapacitors of one or more photo-detectors of the TOF sensor device 202,and calculates capacitance compensation factors that are used by thedistance determination component 208 when determining distanceinformation. In some embodiments, calibration component 210 can also beconfigured to measure other parameter mismatches along the measuringcircuitry, from the photo device to the digital output that provides thevoltage value associated with each capacitor (e.g., the output of theanalog-to-digital converter).

The control output component 212 can be configured to analyze andcontrol one or more sensor outputs based on results generated by thedistance determination component 208. This can include, for example,sending an analog or digital control signal to a control or supervisorydevice (e.g., an industrial controller, an on-board computer mounted ina mobile vehicle, etc.) to perform a control action, initiating a safetyaction (e.g., removing power from a hazardous machine, switching anindustrial system to a safe operating mode, etc.), sending a feedbackmessage to one or more plant personnel via a human-machine interface(HMI) or a personal mobile device, sending data over a safety network,or other such signaling actions. In various embodiments, control outputcomponent 212 can be configured to interface with a plant network (e.g.,a control and information protocol network, and Ethernet/IP network, asafety network, etc.) and send control outputs to other devices over thenetwork connection, or may be configured to send output signals via adirect hardwired connection.

User interface component 214 can be configured to receive user input andto render output to the user in any suitable format (e.g., visual,audio, tactile, etc.). In some embodiments, user interface component 214can be configured to communicate with a graphical user interface (e.g.,a programming or development platform) that executes on a separatehardware device (e.g., a laptop computer, tablet computer, smart phone,etc.) communicatively connected to TOF sensor device 202. In suchconfigurations, user interface component 214 can receive input parameterdata entered by the user via the graphical user interface, and deliveroutput data (e.g., device status, health, or configuration data) to theinterface. Input parameter data can include, for example, normalizedpulse shape data that can be used as reference data for identificationof irregularly shaped pulses, light intensity settings, or other suchparameters. Output data can comprise, for example, status informationfor the TOF sensor device 202, alarm or fault information, parametersettings, or other such information.

The one or more processors 216 can perform one or more of the functionsdescribed herein with reference to the systems and/or methods disclosed.Memory 218 can be a computer-readable storage medium storingcomputer-executable instructions and/or information for performing thefunctions described herein with reference to the systems and/or methodsdisclosed.

FIG. 3 is a diagram of an example architecture for a baselinephoto-detector 302. As will be described herein, photo-detector 302 isreferred to as a baseline photo-detector since additional components canbe added to this baseline architecture to yield other embodiments.Photo-detector 302 can correspond to a single pixel, and can be one ofan array of photo-detectors that make up photo-sensor component 206 ofTOF sensor device 202. Collectively, the array of photo-detectorscapture received pulse signal information that can be used to calculatedistance information for respective pixels of a viewing space beingmonitored by the TOF sensor device 202. The collection of pixel-wisedistance data for the viewing space can yield point cloud informationthat describes a depth or distance topology of the viewing space.Although the present example describes photo-detector 302 as being oneof an array of photo-detectors that make up an imaging sensor device, itis to be appreciated that the techniques carried out by photo-detector302 to measure distance information can also be implemented in asingle-point photo-sensor that generates only a single distance valuefor an object within range of the sensor.

The photo-detector 302 includes a photo device 310 (e.g., a photo-diodeand a capacitor (PD Cap)) that generates and stores electrical chargeswhen exposed to light, such as pulsed light from a reflected pulse aswell as ambient light. The magnitude of the electrical charge isproportional to the intensity of the light incident on the photo device310. The photo device 310 is connected to a first switch 304 enabled byan anti-blooming control (TAB) and a second switch 308 enabled by acapture control line (TX1). Switches 304 and 308 can be transistors orother types of switching devices. The charges stored on the photo device310 are diverted when the TAB switch 304 is active (e.g., when a logicalhigh control signal is applied to the gate of the TAB switch 304),thereby clearing the charges from the photo device 310. The photo device310 is connected to a measuring capacitor (e.g., a floating diffusion(FD) capacitor or another type of measuring capacitor) 306 via thecontrol line TX1.

With this configuration, the charges stored on the photo device 310 canalso be transferred to the measuring capacitor 306 when the TX1 switch308 is active (e.g., when a logical high control signal is applied tothe gate of the TX1 switch 308). The amount of charge stored on themeasuring capacitor 306 (transferred from the photo device 310) can beread by an analog-to-digital converter (ADC) 312 via an amplifier 314,and the ADC 312 converts the magnitude of the charge to a proportionaldigital value representing the amount of charge. In someimplementations, to ensure that a sufficiently high level of charge hasbeen accumulated to yield a high signal value that can be accuratelymeasured, photo-detector 302 may be configured to base the distancemeasurement on a series of received pulses rather than a single receivedpulse. In such implementations, ADC 312 may be configured to read themagnitude of the charge on measuring capacitor 306 after a definednumber of pulses have been received, such that the charge on measuringcapacitor 306 represents an accumulation of a series of pulses. Theaccumulated charge stored on the measuring capacitor 306 can be clearedwhen a logical high control signal is applied to the gate of the reset(RST) transistor 318. The RST transistor 318, control line TX1,measuring capacitor 306, and input of the amplifier 314 are connected tothe same node 316.

Photo-detector 302 can be an element of photo-sensor component 206depicted in FIG. 2. The output of the ADC 312—that is, the digital valuerepresenting the amount of electrical charge on measuring capacitor306—is provided to the distance determination component 208, which usesthe value to calculate the propagation time and corresponding distancefor an emitted light pulse. In some embodiments, as will be discussed inmore detail below, multiple values—obtained using different switchtimings—may be accumulated and read for a signal distance value in orderto accurately estimate the time of the pulse.

As photo-detector 302 receives pulsed light, it develops charges thatare captured and integrated into the measuring capacitor 306. In thisway, each pixel corresponding to a photo-detector 302 generatestime-related information and amplitude information (based on chargevalues) based on received light pulses backscattered by an object in theviewing field illuminated by the emitter component 204.

FIGS. 4A and 4B are a timing diagrams illustrating example timings ofevents associated with operation of photo-detector 302. In general,photo-detector 302 can execute a two-stage measurement that captures atrailing edge portion of a received pulse during the first stage and aleading edge portion of the received pulse during a second stage (orvice versa). The distance determination component 208 can calculate theestimated distance based on a ratio of the trailing edge portion to thefull pulse value (where the full pulse value is the sum of the trailingand leading edges).

FIG. 4A depicts the timing of events for capturing the trailing edgeportion of a pulse during a first stage of the distance measurementcycle (it is to be appreciated, however, that measurement of thetrailing edge portion may instead occur during the second stage of themeasurement cycle, while measurement of the leading edge portion occursduring the first stage). Timing chart 402 represents the timing of thelight pulse output modulated by the TOF sensor device's emittercomponent 204, where the high level of chart 402 represents the time atwhich the emitter component 204 is emitting a light pulse (e.g., lightpulse 416). Timing charts 404 and 406 represent the timings of the TABcontrol signal and the TX1 control signal, respectively (that is, thetiming of the signals applied to the TAB and TX1 control lines). Timingchart 408 represents amount or intensity of light received at the photodevice 310 of the photo-detector 302, where the rise in the chartrepresents receipt of the reflected pulse 412 corresponding to theemitted pulse. Timing chart 410 represents the amount of charge storedon the measuring capacitor 306 over time. The control signals applied tovarious control elements of photo-detector 302 can be controlled inaccordance with control algorithms executed by photo-sensor component206 or distance determination component 208, working in conjunction withthe emitter component 204.

The time at which the TAB control signal goes low and the TX1 controlsignal goes high—referred to as the sampling point or split point—isdefined to be a constant time relative to the time of emission of thelight pulse 416 by the emitter component 204. In the illustratedexample, the sampling point occurs at time t2, which is set to be afixed time relative to the time t1 corresponding to the trailing edge ofthe emitted pulse 416 (the sampling time may also be defined relative tothe leading edge of the emitted pulse 416 in some embodiments). When theTAB control signal goes low and the TX1 control signal goes high at thesampling point (at time t2), the accumulated electrical charge collectedby the photo device 310 in response to received light beginstransferring to the measuring capacitor 306.

As shown in FIG. 4A, the timing of the TAB and TX1 control signalsrelative to the received reflected pulse 412 determines the fraction ofthe total pulse-generated charge that is transferred to measuringcapacitor 306. In the illustrated example, the trailing edge of theemitted pulse 416 leaves the emitter at time t1 (see chart 402). Atsampling time t2 (after a preset delay relative to time t1), the controlsignal on the TAB is turned off, leaving the measuring (FD) capacitor306 discharged, and the control signal on the TX1 switches to ON (seecharts 404 and 406), at which time the measuring capacitor 306 beginsaccumulating charges in proportion to the intensity of the lightreceived at the photo device 310. As shown in chart 408, the reflectedpulse 412 corresponding to the emitted pulse 416 begins being receivedat the photo device 310 some time before time t2 (that is, the risingedge of the reflected pulse 412 is received at the photo device 310before sampling time t2 when the TX1 control signal goes high). Startingat time t2, when the TX1 control signal goes high, the charge on themeasuring capacitor 306 begins increasing in proportion to the level ofreceived light, as shown in chart 410. After receipt of reflected pulse412, the charge quantity V_(1b) transferred to the measuring capacitoris proportional to the shaded area 414 under the received pulse timingchart, which is defined between sampling time t2 and the time when theTX1 control signal goes low. Thus, the charge quantity V_(1b) stored onthe measuring capacitor 306 is proportional to the area of the trailingslice of the reflected pulse 412 captured after sampling time t2, and istherefore function of the position in time of the received pulse 412relative to a calibrated time reference (e.g., the falling edge of theTAB control signal at time t2). Since the time at which the reflectedpulse 412 is received is a function of the distance of the object orsurface from which the pulse 412 was reflected, the amount of thetrailing portion of the reflected pulse that is collected by measuringcapacitor 306 as a fraction of the total received pulse is also afunction of this distance. Accordingly, at the completion of the firststage of the measuring cycle, distance determination component 208stores a value (e.g., voltage V_(1b) or a corresponding value of anelectrical charge) representing the amount of charge stored on measuringcapacitor 306 after completion of the sequence illustrated in FIG. 4A,then initiates the second stage of the measurement cycle depicted inFIG. 4B in order to obtain the leading edge portion.

Similar to the timing sequence depicted in FIG. 4A, FIG. 4B includes atiming chart 418 representing emitted pulse 428 send during the secondstage of the measuring cycle; timing charts 420 and 422 representing thetimings of the TAB control signal and the TX1 control signal,respectively (that is, the timing of the signals applied to the TAB andTX1 control lines during the second stage); a timing chart 424representing the amount or intensity of light received at the photodevice 310, where the rise in the chart represents receipt of thereflected pulse 430 corresponding to the emitted pulse 428; and a timingchart 426 representing the amount of charge stored on the measuringcapacitor 306 over time.

As can be seen by comparing FIGS. 4A and 4B, the timing of events duringthe second stage of the measuring cycle differs from that of the firststage in that emitted pulse 428 is sent at a later time relative to therising edge of the TX1 control signal. This can be achieved by eitherdelaying emission of emitted pulse 428 relative to the first stage, orby switching the TX1 control signal high at an earlier time relative tothe first stage. In the illustrated example, the TX1 control signal isset high prior to emission of emitted pulse 428 (in contrast to thefirst stage depicted in FIG. 4A, in which the TX1 signal goes high afteremission of emitted pulse 416). To ensure that the portion of thereceived pulse that was not captured during the first stage is fullycaptured during the second stage (with little or no overlap between thecaptured leading and trailing portions), the TX1 control signal goeshigh at a time that is earlier by a duration that is substantially equalto the duration of the TX1 high signal. This causes the falling edge ofthe TX1 control signal to occur at substantially the same time—relativethe falling edge of emitted pulse 428—as the rising edge of the TX1controls signal during the first stage (i.e., the difference betweentimes t4 and t3 during the second stage is substantially equal to thedifference between times t2 and t1 during the first stage). This ensuresthat the sampling point at time t4 slices the received pulse 430 atsubstantially the same location as the sampling point at time t2 duringthe first stage. Since the TX1 signal is already set high at the timethe reflected pulse 430 is received, this timing causes the leading edgeportion 432—the portion of the reflected pulse 430 not capture duringthe first stage—to be captured by measuring capacitor 306 as chargequantity V_(1a).

In general, the nearer the object or surface is to the TOF sensor device202, the earlier in time the reflected pulse (pulse 412 or 430) will bereceived, and thus the smaller the trailing portion of the pulse chargethat will be collected by measuring capacitor 306. Accordingly, aftercompletion of the first and second stages of the measuring cycledepicted in FIGS. 4A and 4B, distance determination component 208 cancompute the estimated distance based on the ratio of the measuredtrailing edge portion 414 to the total of the trailing edge portion 414and the leading edge portion 432. For example, the distancedetermination component 208 can calculate the time of flight (orpropagation time) tp for the pulse according to:

$\begin{matrix}{t_{p} = {{\left( \frac{V_{1\; b}}{V_{1\; a} + V_{1\; b}} \right)T_{0}} + T_{S}}} & (2)\end{matrix}$

Where T_(s) is the sampling time relative to the falling edge of theemitted pulse, and T₀ is the duration of the pulse. Note that, inembodiments in which the sampling time is set to coincide with thefalling edge of the emitted pulse, T_(s) will be zero.

In some embodiments, the sequences depicted in FIGS. 4A and 4B arerepeated multiple times per stage in order to accumulate and collect ameasurable amount of charge on the measuring capacitor 306representative of the trailing and leading edge portions. FIG. 5 is atiming diagram illustrating the first stage of the measuring cycledescribed above in connection with FIG. 4A, repeated over a sequence ofmultiple pulses. Execution of multiple measuring cycles is referred toherein as a measuring sequence. As shown in the light pulse timing chartof FIG. 5, a sequence of N light pulses 502 is received at the TOFsensor device's photo-sensor component 206. Light pulses 502 arereflected pulses obtained as a result of emission of a series of pulsesby the TOF sensor device's emitter component 204. After a defined timeduration has elapsed relative to the time of the leading edge of eachemitted pulse 502, the control signal on the TAB goes low and thecontrol signal on the TX1 goes high, causing the measuring capacitor 306to begin collecting the charge from the photo device 310. This charge isa function of the intensity of light received by the photo device 310while the TX1 control signal is high (measuring capacitor 306 is resetand cleared of charges at the beginning of the sequence by applying ahigh signal 512 on the RST control line). The vertical dashed linesrepresent the sampling points 514 at which the TAB control signal goeslow and the TX1 control signal goes high, where these sampling points514 are defined relative to the leading edge of each emitted pulse 502.

As in the example sequence described above in connection with FIG. 4A,the measuring capacitor 306 begins collecting the charge correspondingto a reflected pulse 504 after the leading edge of the reflected pulse504 has reached the photo-sensing component 206. Thus, each time areflected pulse 504 is received by the photo-sensing component 206 anddetected by the photo device 310, the charge on the measuring capacitor306—represented by timing chart 508—increases by an amount proportionalto the shaded region 506 of each received pulse 504 (beginning at thetime that the TX1 control signal goes high). As discussed above, theamount of this shaded region (and thus the amount of charge collected bythe measuring capacitor 306) relative to the amount of the totalreceived pulse is a function of the distance of an object or surfacefrom which the received pulse 504 was reflected. By repeating thismeasuring cycle for the sequence of N pulses, the charges on measuringcapacitor 306 are accumulated over the N received pulses 504 to attain ameasurable quantity of charge with an acceptable signal to noise ratio.The number of pulses N defining this measuring sequence is referred toas the integration number or gating number.

When charges for the N reflected pulses have been accumulated by themeasuring capacitor 306, a read-out signal 510 is activated to trigger areading of the accumulated charge (or a corresponding voltage) from themeasuring capacitor 306. In response to the read-out signal 510, theamount of the accumulated charge stored on the measuring capacitor 306at the end of the sequence is measured or communicated as an analogvalue (e.g., a charge Q or a voltage V), or can be converted into adigital value by ADC 312. The measured value is then provided to thedistance determination component 208 as the measured trailing edgeportion. A similar multiple-pulse sequence can be carried out for thesecond stage illustrated in FIG. 4B in order to accumulate enough chargeto obtain a readable measurement of the leading edge portion, which isalso provided to distance determination component 208, which uses theleading and trailing edge values to determine the propagation time ofthe light pulses and the distance corresponding to the propagation time.

In some embodiments, rather than using the two-stage process describedabove to capture the leading and trailing edges of the received pulse,the process can be modified to capture the trailing edge in one stageand the total pulse in the other stage. The same photo-detectorconfiguration depicted in FIG. 3 can be used for such embodiments;however, the timing of the control signals for the leading edgecollection stage can be modified as shown in FIG. 4C to instead capturethe total reflected pulse. FIG. 4C is a timing diagram illustratingtimings associated with capture of the entirety of reflected pulse 448corresponding to emitted pulse 436. In this example, the TX1 controlsignal goes high prior to receipt of reflected pulse 448, and stays highfor a sufficient duration to capture a charge Q_(T) (corresponding tovoltage V_(T)) proportional to the total reflected pulse 448. That is,charge Q_(T) (or voltage V_(T)) corresponds to the shaded region 448under reflected pulse 448.

In a separate stage of the measuring cycle (either before or aftercapture of the charge Q_(T), V_(T), the trailing edge portion can becaptured as V_(1b) using a timing similar to that illustrated in FIG.4A. With the trailing edge voltage V_(1b) and total pulse voltage V_(T)captured, distance determination component 208 can estimate thepropagation time of the pulse according to:

$\begin{matrix}{t_{p} = {{\left( \frac{V_{1\; b}}{V_{T}} \right)T_{0}} + T_{S}}} & (3)\end{matrix}$

Equation (3) (or a variation thereof) can be used to calculate the timeof flight tp of the emitted pulse if the shape of the pulse issubstantially rectangular (that is, the pulse has very short rise andfall times). If the pulse shape is not rectangular, then a formulaf(V_(1b)/V_(T)) defining the relationship between (V_(1b)N_(T)) and thetime of flight tp can be obtained and approximated, and equation (3) canbe rewritten as:

$\begin{matrix}{t_{p} = {{{f\left( \frac{V_{1\; b}}{V_{T}} \right)}T_{0}} + T_{S}}} & (4)\end{matrix}$

In some alternative embodiments, rather than measuring the trailing andleading edge portions of the received reflected pulse (or the trailingedge portion and total pulse), photo-sensor component may be configuredto measure the trailing edge portion and an amplitude of the receivedpulse, and use these values to estimate the distance. In the case ofsubstantially rectangular received pulses (i.e., pulses withsubstantially flat tops), a proportionality rule can be used to obtainthe ratio of the trailing edge value to the full pulse value based onthe measured trailing edge and the amplitude. Distance determinationcomponent 208 can then translate the ratio to a distance estimate. In avariation of these embodiments in which the received pulses 504 are notsufficiently rectangular, a look-up table can be defined and stored inmemory 218, where the look-up table defines distance valuescorresponding to pairs of trailing edge and pulse amplitude values. Forexample, after determining the trailing edge value and the amplitudevalue, distance determination component 208 can reference the look-uptable to determine the distance value as a function of the trailing edgeand distance values.

The technique described above in connection with FIGS. 3-5 requiremultiple pulses to be received and accumulated—as well as a measurementof the received pulse amplitude—in order to accurately estimatedistance. In order to generate information about the received lightpulses more quickly, thereby improving sensor response time, one or moreembodiments of the TOF sensor device 202 can introduce one or moreadditional measuring capacitors to the baseline photo-detectorarchitecture depicted in FIG. 3. Additional measuring capacitors canalso be used to collect information about ambient light conditions sothat the TOF sensor device 202 can compensate for the effects of ambientlight incident on the photo-receiver array. FIG. 6 is a diagram of anexample architecture of a photo-detector 602 for TOF sensor device 202that includes two measuring capacitors 604 ₁ (FD1) and 604 ₂ (FD2). Thedouble measuring capacitor structure depicted in FIG. 6 allows the TOFsensor device 202 to measure and integrate two parts of the receivedreflected pulse—the trailing part of the pulse and the leading part ofthe pulse—in a single measuring cycle.

In this embodiment, nodes A1 and A2 of the two measuring capacitors 604₁ and 604 ₂ are connected to the photo device 606 via respectiveswitches 610 ₁ and 610 ₂ (e.g., transistors or other types of switchingdevices), which are enabled by signals applied to capture control linesTX1 and TX2. When a high control signal is applied to capture controlline TX1, the charge stored on the photo device 606 is transferred tomeasuring capacitor FD1 604 ₁. Likewise, when a high control signal isapplied to capture control line TX2, the charge accumulated on the photodevice 606 is transferred to measuring capacitor FD2 604 ₁.

Anti-blooming switch 614, which can also be a transistor or other typeof switching device, is also connected to the photo device 606. When ahigh control signal is applied to anti-blooming control line TAB, theaccumulated charge on the photo device 606 is cleared.

Nodes A1 and A2 are also connected to respective ADCs 612 ₁ and 612 ₂via respective amplifiers 616 ₁ and 616 ₂. In response to an instructionfrom the distance determination component 208, the amount of chargestored on measuring capacitor FD1 is converted to a proportional digitalvalue by ADC 612 ₁, the amount of charge stored on second measuringcapacitor FD2 is converted to a proportional digital value by ADC 612 ₂,and the digital values are provided to the distance determinationcomponent 208 for processing. Although FIG. 6 depicts the measuredcharges on measuring capacitors FD1 and FD2 as being read and convertedto digital values by ADC 612 ₁ and 612 ₂, some embodiments may read theamount of charge stored on the measuring capacitors using othertechniques (e.g., by measuring the analog voltage values stored on therespective measuring capacitors). Also, although photo-detector 602 isillustrated as having two separate ADCs—that is, one dedicated ADC foreach measuring capacitor FD1 and FD2—some embodiments may use a singleADC to read and convert the amount of charge on both measuringcapacitors.

Nodes A1 and A2 are also connected to respective reset (RST) lines 608 ₁and 608 ₂. When a high control signal is applied to RST 608 ₁, thestored charge on measuring capacitor FD1 is cleared. When a high controlsignal is applied to RST 608 ₂, the stored charge on measuring capacitorFD2 is cleared.

As with the photo-detector 302 described above, photo-detector 602corresponds to a single pixel of a viewing space being monitored by TOFsensor device 202. In this regard, photo-detector 602 can be one of anarray of photo-detectors 602 that make up a pixel array for the viewingspace. Photo-detector 602 can be an element of photo-sensor component206 depicted in FIG. 2.

FIG. 7 is a timing diagram illustrating an example measuring sequencethat can be carried out in connection with photo-detector 602. Incontrast to photo-detector 302, which uses a single measuring capacitor306 to capture only a trailing portion of a received light pulse (wherethe amount of the captured trailing portion varies as a function of thetime of flight, or propagation delay, of the emitted pulse),photo-detector 602 uses the two measuring capacitors FD1 and FD2 tocapture both the leading and trailing portions of the received lightpulse in a single measuring cycle. That is, the trailing and leadingportions of the received pulse are split between the two measuringcapacitors FD1 and FD2, where the location of the split between the twoportions will be a function of the propagation time of the emittedpulse. The two measurements corresponding to the captured leading andtrailing portions are then used by the distance determination component208 to determine the distance from the TOF sensor device 202 of anobject or surface corresponding to the pixel, using calculationtechniques to be described in more detail herein.

In FIG. 7, the Emitted Light Pulse timing chart represents the magnitudeover time of the modulated light signal controlled by emitter component204, where the emitted pulse 702 is represented by the rise in themagnitude from low to high. The TX1 and TX2 timing charts represent thetiming of the controls signals applied to the TX1 and TX2 control lines(e.g., the gates of the TX1 and TX2 transistors). The Received Pulsetiming chart represents the magnitude or intensity of the light receivedat the photo device 606 of photo-detector 602 over time. The FD1 CapCharge and FD2 Cap Charge timing charts represent the amount ofelectrical charge or voltage stored on the measuring capacitors FD1 andFD2, respectively. That is, FD1 Cap Charge represents the charge orvoltage on node A1 of photo-detector 602, while FD2 Cap Chargerepresents the charge or voltage on node A2.

Though not depicted in the timing diagram of FIG. 7, it is assumed thatthe anti-blooming control line (TAB 614) was pulsed with a high controlsignal prior to the illustrated timing sequence in order to initializethe photo device 606 by removing any previously accumulated electricalcharges. The emitter component 204 of TOF sensor device 202 emits alight pulse 702 into the viewing space. In this example, to ensure thatthe leading portion of the reflected pulse 704 is captured by measuringcapacitor FD1, the control signal of TX1 is set high prior to emissionof the pulse 702. This ensures that the charges accumulated at the photodevice 606 will be transferring charge to measuring capacitor FD1 whenthe reflected pulse 704 corresponding to emitted pulse 702 is received.The control signals applied to various control elements ofphoto-detector 602 can be controlled in accordance with controlalgorithms executed by photo-sensor component 206 or distancedetermination component 208, working in conjunction with the emittercomponent 204.

When the reflected pulse 704 corresponding to emitted pulse 702 isreceived at the photo-detector 602 and detected by the photo device 606,the corresponding charge accumulated in the photo device 606 istransferred to measuring capacitor FD1. Accordingly, as illustrated bythe FD1 Cap Charge timing chart, the electrical charge stored onmeasuring capacitor FD1 increases in proportion with the magnitude ofthe received leading portion of reflected pulse 704 until the samplingtime 706, when the control signal on TX1 goes low and the control signalon TX2 goes high. With the control signal on TX1 set low, the charge onmeasuring capacitor FD1 stops increasing and remains at a constant levelthat is proportional to the first shaded area 708 of the leading portionof reflected pulse 704, defined between the initial rise of the receivedpulse 704 and the sampling time 706.

The sampling time 706 can be defined relative to the time that pulse 702is emitted. For example, TOF sensor device 202 may be configured suchthat the sampling time 706 occurs after a defined interval of timerelative to the leading edge of emitted pulse 702 has elapsed.Alternatively, the time interval may be defined relative to the trailingedge of emitted pulse 702, such that the sampling time 706 occurs aftera defined duration of time subsequent to the trailing edge of theemitted pulse 702.

Since the control signal on TX2 goes high at the sampling time 706 whenthe control signal TX1 goes low, the transfer of charge from the photodevice 606 is redirected from measuring capacitor FD1 to measuringcapacitor FD2. Thus, beginning at the sampling time 706, the chargestored on measuring capacitor FD2 begins increasing from zero until thetrailing edge of the received pulse 704 has been received, or until thecontrol signal on TX2 goes low. In the illustrated example, theelectrical charge on measuring capacitor FD2 increases until theremaining trailing portion of reflected pulse 704 has been completelyreceived, after which the charge levels off to a constant level that isproportional to the second shaded area 710 of the trailing portion ofreflected pulse 704, defined between the sampling time 706 and the endof the reflected pulse 704. The control signal on TX1 goes low after adefined duration after the sampling time 706.

As demonstrated by the generalized timing diagram of FIG. 7, for eachmeasurement cycle of a single emitted pulse, the control signals on TX1and TX2 cause the electrical charge associated with the entire receivedpulse 704 to be divided into two parts—leading and trailing—which arestored separately on internal floating diffusion measuring capacitorsFD1 and FD2. The pulse measuring cycle illustrated in FIG. 7 can berepeated N times for a sequence of N emitted pulses, and the leading andtrailing portion charges on FD1 and FD2 can be accumulated over themultiple N pulses to obtain measurable charges on each measuringcapacitor. The quantity of charge generated and transferred into themeasuring capacitors depends on the strength or intensity of theillumination generated by emitter component 204, the time of exposure ofthe photo-detector 602 for each part of the pulse 708, and the transfertime during which the transfer from the diode of photo device 606 to themeasuring capacitors is enabled. The total time of exposure is theduration of the light pulse that illuminates the scene. The intensity ofthe illumination depends on the amplitude of the current pulse driveninto the light emitter device by the emitter component 204. The transfertime is the duration of the control signals applied to TX1 and TX2 foreach pulse cycle.

At the end of the multiple pulse measuring sequence—comprising Nmeasuring cycles having the timing depicted in FIG. 7—the accumulatedcharges can then be read as voltages on nodes A1 and A2 via ADCs 612 ₁and 612 ₂. These voltages are proportional to the respective percentagesof the leading and trailing portions of the reflected pulse 704 capturedby the two measuring capacitors. The ADCs 612 ₁ and 612 ₂ convert thevoltages to digital values, which are provided to the distancedetermination component and used to calculate the pulse propagation timeand corresponding distance value for the pixel, using computationaltechniques to be described in more detail herein. In general, since thedivision point at which the sampling time 706 intersects with thereflected pulse 704 depends on the time at which the reflected pulse 704is received relative to the time that pulse 702 was emitted, the ratiobetween the leading and trailing portions captured by measuringcapacitors FD1 and FD2 can be used to calculate the propagation time ofthe light pulse and the corresponding distance.

While the pulse measuring cycle illustrated in FIG. 7 describes the useof two separate measuring capacitors—FD1 and FD2—to capture therespective leading and trailing portions of the reflected pulse 704,some alternative embodiments may employ only a single measuringcapacitor to capture both the leading and trailing portions of thereflected pulse 704 using two different measuring sequences. In suchembodiments, the single-capacitor baseline architecture depicted in FIG.3 can be used to capture both leading and trailing portions by varyingthe timing of the signals and other parameters as appropriate. Forexample, a first measuring cycle can capture the leading portion of thepulse by controlling TX1 (the sole control line that controls transferof charge from the photo-device to the sole measuring capacitor) usingthe TX1 control signal timing shown in FIG. 7, whereby the controlsignal is held high from a time prior to emission of the pulse 702 untilthe sampling time 706. This measuring cycle can be repeated for Ncycles, yielding a measurable amount of charge that is proportional tothe leading portion of the received pulse 704. This leading portioncharge can then be read from the measuring capacitor, and the capacitoris cleared. In a subsequent measuring sequence, TX1 is controlledaccording to the TX2 timing shown in FIG. 7, such that the TX1 signalswitches from low to high at the sampling time 706, and is held high fora defined duration that allows the trailing portion of the receivedpulse 704 to be captured. This measuring cycle is repeated for N cyclesto yield a measurable charge proportional to the trailing portion of thereceived pulse 704. This trailing portion charge is then read from themeasuring capacitor, and the capacitor is cleared again.

In the single-capacitor (FIG. 3) and double-capacitor (FIG. 6)embodiments described above, the measured values may be influenced bythe level of ambient light incident on the photo-detector. Depending onthe computational method used to determine the propagation time anddistance, this ambient light can affect the accuracy of the distancecalculations, and therefore should be compensated for when measuring thereceived pulses and calculating the pulse propagation time. Tocompensate for the effects of ambient light, the level of ambient lightcan be captured by the measuring capacitors and measured. In someembodiments, this ambient light measurement can be performed byexecuting a separate measuring sequence without emitting any pulses.Alternatively, in some embodiments, a third measuring capacitor can beadded to the baseline architecture and dedicated to ambient lightmeasurement. FIG. 8 is a diagram of an example architecture of aphoto-detector 802 for TOF sensor device 202 that includes threemeasuring capacitors 804 ₁ (FD1) and 804 ₂ (FD2), and 804 _(A) (FDA). Inthis example, photo device 806, TAB 814, measuring capacitors FD1 804 ₁and FD2 804 ₂, RSTs 808 ₁ and 808 ₂, ADCs 812 ₁ and 812 ₂, and switches810 ₁ and 810 ₂ for control lines TX1 and TX2 have an arrangementsimilar to the corresponding elements of the double-capacitorconfiguration of photo-detector 602. Photo-detector 802 differs from thearchitecture of FIG. 6 by the addition of a third measuring capacitorFDA 804 _(A) and corresponding control line TXA 810 _(A), which are usedto capture the level of ambient light incident on the photo device 806so that the distance determination component 208 can compensate for thisambient light when determining pulse propagation time and objectdistance. A third RST line 808 _(A) is also added to allow the ambientmeasuring capacitor FDA to be cleared of charges. The third measuringcapacitor FDA for ambient light measurement is connected to both ADCs812 ₁ and 812 ₂ via amplifiers 816 ₁ and 816 ₂.

The triple measuring capacitor structure depicted in FIG. 8 allowsambient light to be measured in the same measuring cycle as the pulsemeasurements. The measured amount of ambient light can then besubtracted from the pulse measurements, either in analog prior todigital conversion by the ADCs 812 ₁ and 812 ₂, or digitally after theanalog-to-digital conversion. For example, amplifiers 816 ₁ and 816 ₂may be differential amplifiers that subtract the analog value of thestored charge on measuring capacitor FDA from the respective analogcharges stored on measuring capacitors FD1 and FD2 to yield filteredanalog signals. The differential amplifiers 816 ₁ and 816 ₂ can thenprovide these filtered signals to the respective ADCs 812 ₁ and 812 ₂for conversion to digital values representing the leading and trailingportions of the pulse. Alternatively, amplifiers 816 ₁ and 816 ₂ caneach provide both the analog ambient light value stored on measuring capFDA as well as the respective analog pulse measurements from measuringcapacitors FD1 and FD2 to the ADCs 812 ₁ and 812 ₂. Each ADC can thenconvert both the analog ambient light value and the analog pulse value(either leading or trailing, depending on the ADC) to digital values,and the distance determination component can subtract the digitalambient light value from each of the digital pulse values as a step ofthe distance calculation. In either of these ways, TOF sensor device 202can extract pulse information based only on the captured information forthe leading and trailing parts of the pulse itself without beinginfluenced by ambient light (assuming no saturation).

FIG. 9 is a timing diagram illustrating an example measuring sequencethat can be carried out in connection with photo-detector 802. Timingchart 916 represents the intensity of light received by the photo device806. In addition to the reflected pulse 904 corresponding to emittedpulse 902, the timing chart 916 also depicts the ambient light receivedat the photo device 806 as a constant flat line 914 above zero (ambientlight is assumed to be substantially constant in this example). It isassumed that the anti-blooming control signal to the TAB 814 has beenpulsed prior to the timing shown in FIG. 9 in order to clear the photodevice 806 of charges as an initialization process.

The TX1 and TX2 control signals are controlled in a manner similar tothe timing chart of FIG. 7 for the two-capacitor architecture.Specifically, the TX1 control signal goes high prior to emission ofpulse 902, and remains high until sampling point 906, which is set tooccur a defined duration of time after the leading edge of the emittedpulse 902. While the TX1 control signal is high, the light-drivencharges collected by the photo device 806 are transferred to measuringcapacitor FD1. The TX1 control signal is held high for a definedduration T_(TX1) and is then turned off. As illustrated by the FD1timing chart, when the TX1 control signal goes low at the sampling point906, charges cease transferring to measuring capacitor FD1, and thetotal amount of charge on FD1 levels to a value Q1 (corresponding to avoltage V1). Thus, charge Q1 (and voltage V1) is representative of theleading portion (shaded region 908) of reflected pulse 904 as well asany ambient light received by the photo-detector 802 while the TX1control signal is high. That is, the amount of charge Q1 (or voltage V1)stored on measuring capacitor FD1 is proportional to the shaded region912 of timing chart 916 (representing the amount of ambient lightcollected during the duration of the TX1 high signal) plus the shadedregion 908 (representing the leading portion of the received pulse 904without ambient light).

At the sampling point 906, the TX1 control signal goes low and the TX2control signal goes high, causing the charges from the photo device 806to begin transferring to the second measuring capacitor FD2. The TX2control signal is held high for a duration T_(TX2), and is then switchedlow. The FD2 Cap Charge timing chart illustrates the rise in theaccumulated charge on measuring capacitor FD2 during this durationT_(TX2). When the TX2 control signal goes low, the transfer of charge tomeasuring capacitor FD2 ceases, and the amount of charge on FD2 levelsto a value Q2 (corresponding to voltage V2) representing the trailingportion of received pulse 904 (represented by shaded region 910) plusthe amount of ambient light collected while the TX2 control signal washigh (represented by shaded region 918).

In order to accurately calculate the propagation time of the light pulseand the corresponding distance, the amount of charge corresponding onlyto the shaded regions 908 and 910—the leading and trailing portions ofthe received pulse 904—must be determined. To achieve this, the amountsof charge corresponding to shaded regions 912 and 918—the amount ofambient light received during durations T_(TX1) and T_(TX2)—must beidentified and subtracted from the total amounts of charge Q1 and Q2stored on measuring capacitors FD1 and FD2. By controlling the TX1 andTX2 control signals such that durations T_(TX1) and T_(TX2) are equal(T_(TX1)=T_(TX2)), it can be assumed that the amount of ambient lightcaptured during T_(TX1) and T_(TX2) are approximately equal.Accordingly, if the amount of charge QA representing this amount ofambient light can be determined, this value of QA can be subtracted fromboth Q1 and Q2 to obtain the magnitude of the leading and trailingportions, respectively, of the received pulse 904.

The third measuring capacitor FDA is used to measure QA. As shown on theTXA timing chart in FIG. 9, prior to emission of pulse 902 (and prior toinitiation of the TX1 control signal), photo-sensor component 206 turnson the TXA control signal for a set duration T_(TXA). Setting the TXAcontrol signal high while the emitter component 204 is not emitting apulse ensures that the ambient light measurement will not be distortedby light from the emitter LED. While the TXA control signal is high, thecharges accumulated at the photo device 806 are transferred to theambient light measuring capacitor FDA. The FDA Cap Charge timing chartshows the rise in the amount of charge stored on measuring capacitor FDAas a result of the ambient light received by the photo device 806 duringthis duration T_(TXA). When the TXA control signal goes low, the chargestored on measuring capacitor FDA levels to a constant value QAproportional to shaded region 920 of received light timing chart 916.This charge level represents the amount of ambient light incident on thephoto-detector 802. To ensure that QA is approximately equal to theamount of ambient light captured during durations T_(TX1) and T_(TX2),duration T_(TXA) is set to be equal to T_(TX1) and T_(TX2)(T_(TXA)=T_(TX1)=T_(TX2)).

Once the amount of charge QA is obtained, the amount of charge that isproportional only to the leading portion of the pulse 904 can beobtained according to

Q _(leading) =Q1−QA  (5)

while the amount of charge proportional only to the trailing portion ofthe pulse 904 can be obtained according to

Q _(trailing) =Q2−QA  (6)

Alternatively, the amount of electrical energy corresponding to theleading and trailing portions can be determined using the voltages onthe measuring capacitors rather than charges, as given by:

V _(leading) =V1−VA  (7)

V _(trailing) =V2−VA  (8)

The sum of Q_(leading)+Q_(trailing) (or V_(leading)+V_(trailing))represents the total pulse energy without ambient light (though is notnecessarily equivalent to pulse amplitude alone).

TOF sensor device 202 can determine the values Q_(leading) andQ_(trailing) (or V_(leading) and V_(trailing)) according to equations(5), (6), (7), and/or (8) either prior to conversion by the ADCs 812 ₁and 812 ₂ using the analog values of Q1, Q2, and QA (or V1, V2 and VA)stored on the measuring capacitors, or by first converting the analogvalues of Q1, Q2, and QA (or V1, V2 and VA) to digital values using ADCs812 ₁ and 812 ₂ and implementing equations (5), (6), (7), and/or (8)using the digital values. The photo-detector architecture depicted inFIG. 8 supports calculation of Q_(leading) and Q_(trailing) (orV_(leading) and V_(trailing)) on the analog side. As shown in FIG. 8,the measuring capacitor FDA is connected to inputs of both amplifier 816₁ and amplifier 816 ₂, which are differential amplifiers in thisexample. The measuring capacitor FD1 is connected to the second input ofamplifier 816 ₁, and measuring capacitor FD2 is connected to the secondinput of amplifier 816 ₂. This configuration allows the amplifiers 816 ₁and 816 ₂ to subtract the analog ambient light level QA (or VA) from theanalog values Q1 (or V1) and Q2 (or V2) representing the total energycollected during the T_(TX) and T_(TX2) durations. The analog outputs ofamplifiers 816 ₁ and 816 ₂ are thus proportional to the pulse's leadingand trailing portions, respectively. These analog outputs are providedto the ADCs 812 ₁ and 812 ₂ for conversion to digital values, which arepassed to the distance determination component 208.

FIG. 10 is a diagram of an example architecture of a photo-detector 1002that, similar to photo-detector 802, includes three measuring capacitors—1004 ₁ (FD1) and 1004 ₂ (FD2), and 1004 _(A) (FDA)—for measuring theleading pulse portions, trailing pulse portions, and ambient light,respectively. This configuration allows Q_(leading) and Q_(trailing) (orV_(leading) and V_(trailing)) to be calculated after digital conversionof the measured energy levels. Photo-detector 1002 differs fromphoto-detector 802 in that, rather than connecting measuring capacitorFDA to the same amplifiers 1016 ₁ and 1016 ₂ that measure the charges onmeasuring capacitors FD1 and FD2, measuring capacitor FDA is connectedto a new dedicated amplifier 1016 _(A), the output of which is connectedto a third ADC 1012 _(A). The outputs of ADCs 1012 ₁, 1012 ₂, and 1012_(A) represent digital values of Q1, Q2, and QA (or V1, V2, and VA),which are used by the distance determination component 208 to calculateQ_(leading), Q_(trailing), V_(leading), and/or V_(trailing) according toequations (5), (6), (7), and/or (8).

As yet another alternative embodiment of the three-capacitorconfiguration, the three amplifiers 1016 ₁, 1016 ₂, and 1016 _(A) can beconnected to a single common ADC, with the outputs of the threeamplifiers multiplexed in time. This configuration may be suitable ifcomponent space is limited.

The use of multiple measuring capacitors as in the two-capacitorarchitecture of FIG. 6 or the three-capacitor architectures of FIGS. 8and 10, allows multiple items of pulse information—leading pulseportion, trailing pulse portion, and ambient light—to be collected in asingle measuring sequence. However, it is also possible to obtain thesame multiple items of pulse information using the single-capacitorarchitecture of FIG. 3 by executing multiple consecutive measuringsequences with different timing conditions. For example, a firstmeasuring sequence can be executed whereby ambient light is measuredwhile the emitter remains inactive (not pulses emitted). A secondmeasuring sequence can be executed wherein the TX1 control signalremains high during the entire width of the received pulse, therebymeasuring the total pulse energy including ambient light. A thirdmeasuring sequence can the measure only the trailing portion of thepulse. With these three measured items of data, the trailing portion ofthe pulse can be obtained by subtracting the ambient light measurement(obtained from the first sequence) from the trailing pulse portionmeasurement (obtained from the third sequence). The leading portion ofthe pulse can be obtained by subtracting the ambient light measurementand the calculated trailing pulse portion from the total pulse energyobtained by the second measuring sequence. While requiring fewercapacitors, amplifiers, and ADCs, this technique also requires more timesince three measuring sequences must be executed. The accuracy of thistechnique may also be susceptible to changes in ambient conditions orobject location between sequences.

A number of example TOF photo-detector architectures and correspondingpulse measuring sequences are described above. Methods for estimatingpulse propagation time (time of flight) and corresponding distanceinformation based on the measured pulse information are now described.Any of the calculation techniques described below can be executed by thedistance determination component 208 of TOF sensor device 202, using thedata measured by any of the photo-detector architectures describedabove.

Two general time of flight estimation techniques are described—a ratiomethod and a center of mass method. The ratio method can be performedbased on information collected during a single measuring sequencecarried out by a three-capacitor photo-detector (e.g., photo-detector802 or 1002). The center of mass method—which does not require ambientlight compensation, is less affected by the shape of the pulse, andwhich may be more robust—can be performed using information collectedusing a minimum of two measuring sequences using a two-capacitorphoto-detector (e.g., photo-detector 602). In either estimation method,the accuracy of the estimated time of flight is immune to the effects ofambient light.

The ratio method for determining the propagation time (time of flight)of an emitted light pulse is now described. FIG. 11 is an example timingdiagram illustrating the signal, received light, and measuring capacitorcharge timings for measuring pulse information in accordance with theratio method. A light pulse 1102 is emitted into the viewing field, andthe emitted pulse is reflected and received as received light pulse1110, which causes a corresponding pulse 1104 in the electrical powergenerated by the photo diode of photo device 606. The electrical energygenerated in the photo diode as a result of received pulse 1110 is splitinto two portions—the leading portion (represented by shaded region 1112of electrical pulse 1104) stored in measuring capacitor FD1 as voltageV1, and the trailing part (represented by shaded region 1108 ofelectrical pulse 1104) stored on measuring capacitor FD2 as voltage V2(as shown in the FD1 Cap Charge and FD2 Cap Charge timing charts in FIG.11). The split point or sampling point 1106 is defined by the fallingedge of the TX1 control signal and rising edge of the TX2 controlsignal.

Time duration T₀ is the usable part of the received electrical pulse1104; that is, the portion of the pulse 1104 between the leading andtrailing edges from which pulse information can be reliably obtained.This allows a distance range coverage of:

Range=cT ₀/2  (9)

Assuming the emitted pulse 1102 is substantially rectangular (that is,flat in the middle, usable part of the electrical pulse 1104 withnegligible rise and fall times at the leading and trailing edges) andthe split point at the sampling point 1106 is far from the edges of thereceived pulse 1104, the quantity of charges transferred into measuringcapacitor FD2 (having capacitance C2) varies linearly with the delay tpof the received pulse 1104, defined as the duration of time between thesampling point 1106 and the end of the usable portion of the receivedpulse 1104. This delay tp is also a function of the total propagationtime (time of flight) of the emitted pulse.

Assuming the time reference is t=0 in the case whereby the falling edgeof the pulse is just after the sampling point 1106 between the TX1 andTX2 control signals, then tp is proportional to the charge Q2 integratedinto measuring capacitor FD2. Since charge Q2 is the product ofcapacitance C2 and voltage V2 on the measuring capacitor FD2, tp is alsoproportional to the output voltage V2. Similarly, the time (T₀−tp) isproportional to the charge Q1 stored on measuring capacitor FD1 (havingcapacitance C1). As such, Q1 and Q2 can be expressed by the followinglinear equations:

$\begin{matrix}{{Q\; 2} = {{C\; 2\; V\; 2} = {{\frac{t_{p}}{T_{0}}{Qu}} + {QA}}}} & (10) \\{{Q\; 1} = {{C\; 1\; V\; 1} = {{\frac{T_{0} - t_{p}}{T_{0}}{Qu}} + {QA}}}} & (11)\end{matrix}$

where Qu is the proportionality ratio defined by:

Qu=C1V1+C2V2−2QA  (12)

Proportionality ratio Qu, which is the amount of charge representing thesum of the leading and trailing portions of received pulse 1104 with thecharge representing ambient light 2QA removed, is proportional to thesum of shaded regions 1112 and 1108 in FIG. 11. In order to obtain thevalue of QA, the third measuring capacitor FDA (having capacitance CA)can be used to measure the charges generated by ambient light prior toemission of light pulse 1102 (as described above in connection withFIGS. 8-10), or during a time after receipt of the reflected pulse whileonly ambient light is being received. Mismatch between capacitance C2relative to C1, and between capacitances CA relative to C1, can bemeasured and compensated for during a calibration process to bediscussed in more detail herein.

After the photo-detector has measured values for V1, V2, and VA usingany of the measuring sequences described above, the measured values canbe used to determine the delay tp. The amount of charge QA stored onmeasuring capacitor FDA, representing the measured amount of ambientlight while no light pulses are being emitted, is given by:

QA=CA VA=βC1VA  (13)

where CA is the capacitance of measuring capacitor FDA, C1 is thecapacitance of measuring capacitor FD1, β=CA/C1 (a compensation factorthat compensates for capacitance mismatch between measuring capacitorsFDA and FD1), and VA is the voltage stored on measuring capacitor FDA asa result of the stored charge QA.

The amount of charge Q2 stored on measuring capacitor FD2, representingthe trailing portion of the received pulse 1104 between the samplingpoint 1106 and the end of the usable portion of the pulse 1104, is givenby:

Q2=C2V2=αC1V2  (14)

where C2 is the capacitance of measuring capacitor FD2, α=C2/C1 (acompensation factor that compensates for capacitance mismatch betweenmeasuring capacitors FD2 and FD1) and V2 is the voltage stored onmeasuring capacitor FD2 as a result of the stored charge Q2.

The delay tp can then be given by:

$\begin{matrix}{t_{p} = {{\frac{{\alpha \; V\; 2} - {\beta \; V_{A}}}{{{V\; 1} +} \propto {{V\; 2} - {2\; \beta \; V_{A}}}}T_{0}} + T_{S}}} & (15)\end{matrix}$

The ratio of the propagation time tp to the total pulse duration T₀ isthe same as the ratio of the captured trailing edge energy to the totalpulse energy (leading plus trailing portions). Therefore, as given byequation (15), propagation time tp is determined by identifying thefraction of the total pulse energy without ambient light(V1+∝V2−2βV_(A)) that is attributed to the measured trailing portionwithout ambient light (αV2−βV_(A)), and multiplying this fraction by thetotal duration T₀ of the pulse.

Alternatively, the value of tp can also be calculated based on theleading portion of the pulse using the value of V1:

$\begin{matrix}{{T_{0} - t_{p}} = {{\frac{{V\; 1} - {\beta \; V_{A}}}{{{V\; 1} +} \propto {{V\; 2} - {2\; \beta \; V_{A}}}}T_{0}} + T_{S}}} & (16)\end{matrix}$

In this case, the ratio of the leading edge energy to the total pulseenergy is the same as the ratio of (T₀−tp) to the total pulse durationT₀.

The value of tp can also be calculated based on a combination ofequations (15) and (16):

$\begin{matrix}{t_{p} = {{\left( {1 + \frac{{\alpha \; V\; 2} - {V\; 1}}{{{V\; 1} +} \propto {{V\; 2} - {2\; \beta \; V_{A}}}}} \right)\frac{T_{0}}{2}} + T_{S}}} & (17)\end{matrix}$

With the capacitance mismatch compensation factors α and β obtained viacalibration (described in more detail below), obtaining the threevoltage values V1, V2, and VA at the end of a measuring sequence of Npulses (integrations), as described in the foregoing examples, allowsthe distance determination component 208 to estimate the pulse delaytime td using any of equations (15), (16), or (17) (or reasonablevariations thereof). The distance determination component 208 can thenuse this delay value tp in equation (1) to determine the distance d ofthe object or surface corresponding to the pixel, as given by:

d=(c/2)t _(p)  (18)

While the calculation techniques represented by equations (15), (16), or(17) rely on a substantially rectangular pulse with negligible rise andfall times, these calculation methods can be generalized for cases inwhich the rise time and fall times of the received pulse are notnegligible, or when the pulse has an irregular non-rectangular shape, aswill be described in more detail herein.

As noted above, equations (15), (16), or (17) rely on compensationfactors β and α, which represent the capacitance ratios CA/C1 and C2/C1,respectively. While the capacitances of the three measuring capacitorsFD1, FD2, and FDA are ideally equal (which would make the compensationfactors β and α equal to 1), there is a likelihood of mismatch betweenthe capacitances, which can be measured and compensated for in equations(15)-(17). Therefore, in one or more embodiments, the TOF sensor device202 can include a calibration component 210 (see FIG. 2) configured tocalibrate the relative values of measuring capacitors FD1 and FD2. Thecalibration component 210 can calibrate these relative values using twomeasuring cycles per measuring capacitor, yielding a total of four datapoints—(V1 a, V1 b) for measuring capacitor FD1, and (V2 a, V2 b) formeasuring capacitor FD2.

FIG. 12 is a timing diagram illustrating measurement of these fourcalibration data points during the calibration sequence. The timings ofthe TX1 and TX2 control signals, as well as the timing of emission oflight pulses 1202 a and 1202 b, can be controlled by calibrationcomponent 210, in coordination with emitter component 204 andphoto-sensor component 206. In this example sequence, two light pulses1202 a and 1202 b corresponding to two consecutive measurement cyclesare emitted by emitter component 204, resulting in two reflected pulses1204 a and 1204 b received at photo-sensor component 206. The firstmeasuring cycle begins at time 1212 a, and the second measuring cyclebegins at time 1212 b (where a measurement and a reset is performed atthe end of the first measuring cycle at time 1216, and anothermeasurement and reset is performed at the end of the second measuringcycle at time 1218). For each reflected pulse 1204 a and 1204 b, the TX1and TX2 control signals are controlled to capture charges correspondingto the leading and trailing portions of the pulse in measuringcapacitors FD1 and FD2, using a control signal timing similar to thatdescribed in previous examples. Although FIG. 12 depicts only a singlepulse being emitted and received within each measuring sequence forclarity, some embodiments may emit and receive multiple pulses withineach measuring cycle, performing an accumulation and measurement over asequence of N pulses within each sequence.

For the measurement of the first received pulse 1204 a during the firstmeasuring cycle, the sampling point 1206 a is set to occur after a firstdefined duration after the start time 1212 a of the first measuringcycle. As shown in the FD1 Cap Charge and FD2 Cap Charge timing charts,the leading portion of the first received pulse 1204 a is stored onmeasuring capacitor FD1 as value V1 a, and the trailing edge of thereceived pulse 1204 a is stored on measuring capacitor FD2 as value V2a. These values can be read out and stored by the calibration component210 prior to the beginning of the second measuring cycle.

In general, the charge Q1 on measuring capacitor FD1 can be given as:

$\begin{matrix}{{Q\; 1} = {{C\; 1\; V\; 1} = {{\frac{T_{0} - t_{p}}{T_{0}}{Qu}} + {QA}}}} & (19)\end{matrix}$

As noted above, the charge Qu is the amount of charge representing thesum of the leading and trailing portions of received pulse, notincluding ambient light. The amount of this charge Qu that isproportional to the leading portion of the pulse 1204 a is a fraction ofQu corresponding to a ratio of the leading part time duration (T₀−tp) tothe total duration of the pulse T₀. Adding the ambient light charge QAto this fraction of Qu yields the total charge Q1 (or C1V1), as given byequation (18).

The voltage level V1 corresponding to this charge can be given as:

$\begin{matrix}{{V\; 1} = {{{- \frac{QA}{C\; 1\; T_{0}}}t_{p}} + \frac{{QA} + Q_{u}}{C\; 1}}} & (20)\end{matrix}$

The charge Q2 on measuring capacitor FD2 can be given as:

$\begin{matrix}{{Q\; 2} = {{C\; 2\; V\; 2} = {{\frac{t_{p}}{T_{0}}{Qu}} + {QA}}}} & (21)\end{matrix}$

The voltage level V2 corresponding to this charge can be given as:

$\begin{matrix}{{V\; 2} = {{\frac{Q_{u}}{C\; 2\; T_{0}}t_{p}} + \frac{QA}{C\; 2}}} & (22)\end{matrix}$

Given these relationships, the captured charges Q1 a and Q2 acorresponding to the leading and trailing portions of the first pulse1204 a captured during the first measuring cycle of the calibrationsequence are given by:

$\begin{matrix}{{Q\; 1\; a} = {{C\; 1\; V\; 1\; a} = {{\frac{T_{0} - t_{p}}{T_{0}}{Qu}} + {QA}}}} & (23) \\{{Q\; 2\; a} = {{C\; 2\; V\; 2\; a} = {{\frac{t_{p}}{T_{0}}{Qu}} + {QA}}}} & (24)\end{matrix}$

and the charge Qu corresponding to ambient light is given by:

Qu=C1V1a+C2V2a−2QA  (25)

After the first measurement, the calibration component 210 can recordthe values of V1 a and V2 a, then clear the charges from the measuringcapacitors FD1 and FD2 prior to emission of the second light pulse 1202b in order to initialize the measuring capacitors for the secondmeasuring cycle.

For the second measuring cycle (beginning a time 1212 b), the secondpulse 1202 b is emitted at a delayed time Td within the measuring cyclerelative to the time of emission of the first pulse 1202 a with thefirst measuring cycle. That is, whereas the time 1210 of the leadingedge of the first pulse 1202 a occurs a first duration after the starttime 1212 a of the first measuring cycle, the time 1214 of the leadingedge of the second pulse 1202 b occurs a delayed time Td longer than thefirst duration after the start time 1212 b of the second measuringcycle, where Td is a fraction of the pulse period T₀. As a result ofthis delay, the sampling point 1206 b for the second measuringsequence—which occurs at the same time relative to the start time 1212 bof the second measuring sequence as the first sampling point 1206 arelative to the start time 1212 a of the first measuring sequence—splitsthe second received pulse 1204 b at a time Td sooner than the split ofthe first received pulse 1204 a by the first sampling point 1206 a ofthe first measuring cycle. Thus, as shown in FIG. 12, sampling point1206 a of the first measurement occurs at a time tp prior to the end ofthe usable part of the trailing portion of the first received pulse 1204a, and sampling point 1206 b occurs at a time (Td+tp) prior to the endof the usable part of the trailing portion of the second received pulse1204 b.

For the second measuring cycle, captured charges Q1 a and Q1 bcorresponding to the leading and trailing portions of the second pulse1204 b of the calibration sequence are given by:

$\begin{matrix}{{Q\; 1\; b} = {{C\; 1\; V\; 1\; b} = {{\frac{T_{0} - t_{p} - T_{d}}{T_{0}}{Qu}} + {QA}}}} & (26) \\{{Q\; 2\; b} = {{C\; 2\; V\; 2\; b} = {{\frac{t_{p} + T_{d}}{T_{0}}{Qu}} + {QA}}}} & (27)\end{matrix}$

and the charge Qu corresponding to ambient light is given by:

Qu=C1V1b+C2V2b−2QA  (28)

From equations (23)-(28), the ratio α between capacitances C1 and C2 ofthe measuring capacitors FD1 and FD2 can be determined using the capturevalues V1 a, V1 b, V2 a, and V2 b according to:

$\begin{matrix}{\propto {= {\frac{C\; 2}{C\; 1} = \frac{{V\; 1\; a} - {V\; 1\; b}}{{V\; 2\; b} - {V\; 2\; a}}}}} & (29)\end{matrix}$

Calibration component 210 can determine this mismatch ratio α accordingto equation (29), and provide the calibrated ratio to distancedetermination component 208 for use in any of equations (15)-(17). Invarious embodiments, calibration component 210 can be configured toperform the calibration sequence described above during a designatedcalibration sequence that occurs once (e.g., during a power-up sequenceof TOF sensor device 202 or in response to initiation of the sequence bythe user), or that occurs periodically in order to update the mismatchratio α during operation (e.g., periodically or during measurementsequences).

The measurement and calculation technique described above in connectionwith FIG. 11 demonstrates the ratio method for estimating time of flightand generating distance information using the photo-detectorarchitectures described herein. The center of mass method, analternative technique to the ratio method for determining time of flightusing these photo-diode architectures, is now discussed. As noted above,the center of mass method can be performed using information collectedfrom a minimum of two measuring sequences using a two-capacitorphoto-detector (e.g., photo-detector 602). The center of mass techniquecan be particularly suitable for achieving good distance estimationprecision when long light pulses are used, or when the pulse shape isnot substantially rectangular (i.e., if the received pulse has asignificantly long rise time and/or fall time). The center of masstechnique does not require ambient light to be measured, making thistechnique suitable for the two-capacitor photo-detector architectureillustrated in FIG. 6.

FIG. 13A is an example timing diagram illustrating the signal, receivedlight, and measuring capacitor charge timings for measuring pulseinformation in accordance with the center of mass method. In thisexample timing, two measuring sequences are carried out. In the firstmeasuring sequence, pulse 1302 a is emitted, and the charges generatedby the corresponding received pulse 1304 a are split into leading andtrailing portions between measuring capacitors FD1 and FD2, as describedin previous examples (see, e.g., FIG. 7 and the correspondingdescription).

At the end of this first measuring sequence, the voltage V_(c1a) onmeasuring capacitor FD1 and V_(c2a) on measuring capacitor FD2 representthe leading and trailing portions, respectively, of received pulse 1304a relative to the time 1306 a of the sampling point (including anyambient light also collected during the leading and trailing portionmeasurements). During the first measuring sequence, light pulse 1302 amay be emitted N times, with the leading and trailing portions of thecorresponding received pulse 1304 a being integrated over N measuringcycles to yield measurable values of V_(c1a) and V_(c2a). Each cyclebegins at time 1310 a, when the TX1 control signal goes high. For eachof these N cycles, pulse 1302 a is emitted after a fixed time delayafter the start time 1310 a of the cycle, such that the time 1306 a ofthe sampling point occurs at a time tp prior to the trailing edge of theusable portion of the received pulse 1304 a (for clarity, the timingdiagram illustrated in FIG. 13A assumes that N=1, such that only asingle measuring cycle is performed prior to initiation of the secondmeasuring sequence). As in previous examples, the timing of the emittedpulse 1302 a and the TX1 and TX2 control signals can be controlled bythe emitter component 204 and photo-sensor component 206, respectively.

Prior to the second measuring sequence, the voltage values V_(c1a) andV_(c2a) are recorded by the distance determination component 208 (e.g.,by reading the voltage values via amplifiers 616 ₁ and 616 ₂ and ADCs612 ₁ and 612 ₂), and the stored charges on the measuring capacitors arecleared by setting a rest pulse 1312 on the RST lines. For the secondmeasuring sequence, which begins at time 1310 b when the TX1 controlsignal goes high, light pulse 1302 b is emitted, and the leading andtrailing portions of the charge generated by the corresponding receivedpulse 1304 b are accumulated in measuring capacitors FD1 and FD2 asvoltages V_(c1b) and V_(c2b), respectively, as described in previousexamples. As in the first measuring sequence, pulse 1302 b can beemitted N times, resulting in N measuring cycles. For each of the Ncycles of this second measuring sequence, pulse 1302 b is emitted laterin the cycle relative to the first pulse 1302 a by a delay time T₁(which is less than the total period T₀ of the received pulse 1304 b).That is, if pulse 1302 a is emitted at after a time duration x haselapsed after the leading edge of the TX1 signal of the first measuringcycle, pulse 1302 b is emitted after a time duration (x+T₁) has elapsedafter the leading edge of the TX1 signal of the second measuring cycle.This causes the sampling time 1306 b to occur at a time (T₁+tp) prior tothe trailing edge of the received pulse 1304 b. At the end of the Nmeasuring cycles, the distance determination component 208 reads thevoltage values V_(c1b) and V_(c2b). The voltage values represent theleading and trailing portions of the received pulse 1304 b as divided bythe sampling point defined by time 1306 b.

FIG. 14 is a chart plotting the four measured voltages V_(c1a), V_(c2a)V_(c1b), and V_(c2b) as a function of the emission time the pulserelative to the start of the measuring sequence. Since the voltagelevels respectively associated with the leading and trailing portions ofthe pulse vary linearly as a function of the emission time relative tothe start of the measuring sequence, a straight line 1402 connectingvoltage data points V_(c1a) and V_(c1b) (the measured leading portionsfor the two measuring sequences) represents the leading portion voltageas a function of pulse emission time. Similarly, a straight line 1404connecting voltage data points V_(c2a) and V_(c2b) represents thetrailing portion voltage as a function of the pulse emission time.

The distance in the x-axis direction between the data points of thefirst measuring sequence (V_(c1a) V_(c2a)) and the data points of thesecond measuring sequence (V_(c1b) and V_(c2b)) is the time delay T₁.The time difference between the mid-point (CM0) of this duration T₁ andthe intersection point (CM) between lines 1402 and 1404 is taken to bethe delay tp (the time between the sampling point of the first measuringsequence and the trailing edge of the pulse 1304 a).

Accordingly, distance determination component 208 can calculate the timeof flight tp using measured voltages V_(c1a), V_(c2a) V_(c1b), andV_(c2b) according to

$\begin{matrix}{t_{p} = {\frac{\left( {V_{c\; 1\; a} - V_{c\; 2\; a}} \right) - \left( {V_{c\; 2\; b} - V_{c\; 1\; b}} \right)}{\left( {V_{c\; 1\; a} - V_{c\; 2\; a}} \right) + \left( {V_{c\; 2\; b} - V_{c\; 1\; b}} \right)}\frac{T_{1}}{2}}} & (30)\end{matrix}$

where T₁ is the time difference between the two emitted pulses 1302 aand 1302 b relative to the sampling point, and tp is the time of flightof the pulse. Equation (30) can also be written as

$\begin{matrix}{{t_{p} = {\frac{{\Delta \; V_{ca}} - {\Delta \; V_{cb}}}{{\Delta \; V_{ca}} + {\Delta \; V_{cb}}}\frac{T_{1}}{2}}}{where}} & (31) \\{{{\Delta \; V_{ca}} = \left( {V_{c\; 1\; a} - V_{c\; 2\; a}} \right)}{and}} & (32) \\{{\Delta \; V_{cb}} = \left( {V_{c\; 2\; b} - V_{c\; 1\; b}} \right)} & (33)\end{matrix}$

Note that (V_(c1a)+V_(c2a))=(V_(c2b)+V_(c1b)), and(V_(c1a)−V_(c1b))=(V_(c2b)−V_(c2a)).

More generally, the time of flight can be determined using the center ofmass method based on the following base formula:

$\begin{matrix}{t_{p} = {\frac{T_{sb} + T_{sa}}{2} + {\frac{\left( {v_{c\; 1\; a} - v_{c\; 2\; a}} \right) - \left( {v_{c\; 2\; b} - v_{c\; 1\; b}} \right)}{\left( {v_{c\; 1\; a} - v_{c\; 2\; a}} \right) + \left( {v_{c\; 2\; b} - v_{c\; 1\; b}} \right)}\frac{T_{1}}{2}}}} & (34)\end{matrix}$

where T₁=T_(sb)−T_(sa), and T_(sa) and T_(sb) are the times of the twosampling points 1306 a and 1306 b.

In equations (30), (31), and (34), differentialΔV_(cb)=(V_(c2b)−V_(c1b)) is the voltage differential between thetrailing portion voltage and the leading portion voltage for the secondmeasuring sequence, and differential ΔV_(ca)=(V_(c2a)V_(c1a)) is thevoltage differential between the trailing portion voltage and leadingportion voltage for the first measuring sequence. Obtaining the ratio ofthe difference between these two voltage differentials to the sum of thetwo voltage differentials, and multiplying this ratio by half the delayT₁ yields the propagation time tp for the pulse. In general, thepropagation time tp is determined based on an amount by which thedifference between the leading and trailing portions changes between thefirst measuring cycle and the second measuring cycle.

Once the distance determination component 208 has calculated a value oftp based on equation (31) (or variations thereof), the distancedetermination component 208 calculates distance associated with thepixel (that is, the distance of an object or surface within the viewingspace corresponding to the photo-detector's pixel) using this value oftp as the propagation time tin equation (1). The possible distance rangeusing the center of mass method is +/−dr relative to center of range, or+/−T₁/2 in time.

Equations (31) and (34) assume that the capacitances C1 and C2 of themeasuring capacitors are equal. However, in some cases the capacitancesmay differ, but the difference can be measured as a ratio ∝=C2/C1 usingthe calibration process described above and applied as a correctionfactor (e.g., by multiplying Vc2 a and Vc2 b in equations (31) and (34)by calibration factor ∝).

Since the center of mass technique is based on the differentials betweenthe leading and trailing portion voltages, and in particular the ratioof these differentials between the first and second measuring sequences,the inclusion of ambient light in measured voltages V_(c1a), V_(c2a)V_(c1b), and V_(c2b) does not adversely affect the accuracy of the tpcalculation. Since the portions of the voltages attributable to ambientlight can reasonably be assumed to be the same for all four voltages,the presence of this ambient light voltage in all four voltage datapoints does not change the differentials between the leading andtrailing portions.

The ratio and center of mass techniques described above assumes asubstantially rectangular light pulse. For scenarios in which the shapeof the received light pulse is not rectangular, there is no directformula to express the pulse time of flight based on the V1 and V2measurements. However, in some embodiments in which a non-rectangular orirregularly shaped light pulse is used, the TOF sensor device 202 canuse a variation of the ratio method that relies on knowledge of thepulse shape acquired during a calibration or teaching process. In suchembodiments, the pulse shape can be stored as a normalized look-uptable, or in any other suitable format. In particular, the calibrationcomponent 210 can store the integral of the pulse as measured frommeasuring capacitors FD1 and FD2 for different integration times.

This variation of the ratio method can be used with the three-capacitorconfiguration depicted in FIG. 8 or 10. As described above in connectionwith those three-capacitor configurations, measured values of V1, V2,and VA—representing the measured leading, trailing, and ambient portionsof the received pulse—are obtained using the signal timing describedabove in connection with FIG. 9 (though in contrast to that example, theemitted and received pulse is assumed to be an irregular,non-rectangular pulse). From these values of V1, V2, and VA, thedistance determination component 208 (or the photo-sensor component 206)can derive normalized values v1 and v2 as follows:

$\begin{matrix}{{v\; 1} = \frac{V\; 1}{{{V\; 1} +} \propto {{V\; 2} - {2\; \beta \; V_{A}}}}} & (35) \\{{v\; 2} = \frac{\alpha \; V\; 2}{{{V\; 1} +} \propto {{V\; 2} - {2\; \beta \; V_{A}}}}} & (36)\end{matrix}$

Since equations (35) and (36) normalize the measured voltages V1 and V2as fractions of the total leading and trailing portion voltagesattributable to the pulse (without ambient light), v1+v2=1 due to thenormalization.

FIG. 15 is a plot representing a light pulse shape reference. The datapoints 1502 represent values of the measuring capacitor voltage(proportional to the intensity or magnitude of the received light pulse)as a function of time. FIG. 16 is a plot representing normalizedreference pulse integrals of the reference pulse plot of FIG. 15, whereplot 1602 represents normalized voltages v1 corresponding to measuringcapacitor FD1 (having capacitance C1) as a function of propagation timetp, and plot 1604 represents normalized voltages v2 corresponding tomeasuring capacitor FD2 (having capacitance C2) as a function ofpropagation time tp. These normalized values of v1 and v2 can be stored(e.g., on memory 218) as a look-up reference table or in anothersuitable format. As shown in FIG. 16, the distance determinationcomponent 208 can determine the time position of the received pulse fromeither v1 or v2 by calculating one or both of v1 or v2 using equations(35) and/or (36), and determining the value of tp corresponding to v1and/or v2 by referencing this look-up table. Since the data stored inthe reference look-up table does not require the light pulse to berectangular, this variation of the ratio method can be used forembodiments of TOF sensor device 202 that use irregular, non-rectangularpulses.

In some embodiments, plots 1602 and/or 1604 can be obtained throughmeasurement and entered into TOF sensor device 202 (e.g., via userinterface component 214)

A variation of the center of mass calculation method that can be usedwith non-rectangular pulses is now described. When the shape of thereceived light pulse is not rectangular, the integral of the pulse isnot linear and there is no direct formula to express the pulse time offlight based on the V1 a, V2 a and V1 b, V2 b measurements discussedabove. Consequently, as with the alternative ratio method describedabove, predefined knowledge of the pulse shape acquired during acalibration or teaching sequence can be relied upon to determine time offlight tp. To this end, the integral of the pulse shape can be stored(e.g., on memory 218) as normalized look-up table data, which can bereferenced by distance determination component 208 to situate the pulse(delay) relative to the trigger point.

The values of the measurement points (V1 a, V2 a and V1 b, V2 b)relative to the corresponding point on the reference (normalized)integral curve is dependent upon the pulse amplitude (or gain factor)and on bias due to ambient light. This can be described by

V=kv+V _(A)  (37)

where V is the measured voltage (e.g., V1 a, V2 a, V1 b, or V2 b), k isthe amplitude or gain factor of the pulse, v is the normalized voltage(ranging from 0 to 1), and V_(A) is the voltage corresponding to thelevel of ambient light. Note that k and V_(A) will be the same for eachof the four measured voltages V1 a, V2 a, V1 b, and V2 b.

There are three unknowns to be resolved or eliminated in order tocalculate tp—ambient light level, pulse amplitude k and the pulse delaytp itself. The process for estimating the pulse delay tp is the processof minimizing the distance d of the four adjusted measurements relativeto the reference pulse integral curves. This can be achieved using thefollowing generalized steps:

1) Remove the ambient light, and use v1 a−v2 a=(V1 a−V2 a)/k and v1 b−v2b=(V1 b−V2 b)/k in a search iteration algorithm.

2) Using the search algorithm, adjust pulse delay tp and the pulseamplitude k in order to minimize the distance to the reference pulseintegral curves of v1 a and v1 b according to

$\begin{matrix}{{v\; 1_{a}} = {\frac{1}{2}\left( {1 + \frac{{V\; 1_{a}} - {V\; 2_{a}}}{k}} \right)}} & (38) \\{{v\; 1_{b}} = {\frac{1}{2}\left( {1 - \frac{{V\; 2_{b}} - {V\; 1_{b}}}{k}} \right)}} & (39)\end{matrix}$

FIG. 17 is a chart that plots the normalized reference pulse integraldata (similar to the chart of FIG. 16). In an example implementation,the iterative algorithm can seek to minimize the following costfunction:

d=(v1_(a) −V _(a))²+(v1_(b) −v _(b))²  (40)

where va and vb are the points on the reference integral for a givenvalue of tp. The distance determination component 208 can execute theiterative algorithm to find values of v1 a and v1 b that minimize thedistance d, and these values can be used to determine the value of tp.The chart illustrated in FIG. 17 indicates the values of v1 a, v1 b, andtp at the end of the iterative search and minimization process.

FIG. 18 is a flowchart illustrating the general steps of the iterativeprocess. At 1802, values of tp and k are selected. At 1804, the storednormalized reference pulse integral data is referenced to determine thevalues of va and vb corresponding to the selected value of tp. At step1806, the value of distance d is determined according to equation (40)using the referenced values of va and vb, and the values of v1 a and v1b obtained using equations (38) and (39) the selected value of k. Atstep 1808, based on the value of d, the value of k is modified, andsteps 1802-1806 are repeated using the modified value of k. Steps1802-1808 are repeated in an iterative fashion until values of v1 a andv1 b that minimize or substantially minimize the value of d in equation(40) are obtained.

In the case of the center of mass method, the range of pulse arrivaltime that can be measured is from T_(s) to (T_(s)+T₀). This means thatthe range covered for a pulse having a duration of T₀=20 nanoseconds(ns) is three meters wide (d=c/2·T₀) starting from the positioncorresponding to T_(s). Since the precision of the distance measurementis more precise with a smaller pulse, it is preferable to avoidincreasing the pulse duration T₀ to cover a wider range. Instead, awider range can be obtained by performing multiple measurements—witheach measurement covering contiguous subranges—and combining results ofthe multiple measurements. For example, with the same pulse of 20 nsduration, two measuring sequences offset by 20 ns (corresponding tothree meters) from each other can increase the measurable range toapproximately six meters. FIG. 11B is a timing chart illustrating TX1and TX2 switch timings for two example measuring sequences that can becombined to extend the measurable distance. The first measuringsequence—sequence A—has a sampling time T_(sa)=0 (that is, the TX1control signal goes low and the TX2 control signal goes high at a timesubstantially corresponding to the falling edge of emitted pulse 1114)for a range of 0 to 3 meters. The second measuring sequence—sequenceB—has a sampling time T_(sb)=20 ns (whereby the Tx1 signal goes low andthe TX2 signal goes high 20 ns after the falling edge of the emittedpulse 1114) for a range of 3 to 6 meters.

Note that the sampling time T_(sb) for measuring sequence B is delayedrelative to the sampling time T_(sa) for measuring sequence A byapproximately the pulse duration T₀. That is, the duration between thefalling edge of the emitted light pulse and sampling time T_(sb) in thesecond measuring sequence is greater than the duration between thefalling edge of the emitted pulse and sampling time T_(sa) in the firstmeasuring sequence by approximately T₀. This ensures that the measurableranges of the two sequences are contiguous (0-3 meters for the firstsequence, and 3-6 meters for the second sequence).

According to the center of mass method, the range that can be measuredranges from T_(sb) to (T_(sa)+T₀). As discussed previously, the centerof mass method requires two measuring sequences, each providing twoitems of pulse data (V₁, V₂) captured from each of the sampling pointsT_(sa) and T_(sb). As an example, with the same 20 ns pulse and 10 nsbetween the two sampling points T_(sa) and T_(sb), a center of massrange from 1.5 meters to 3 meters can be achieved. FIG. 13B is a timingdiagram illustrating TX1 and TX2 switch timings for two measuringsequences in which the sampling time T_(sb) for measuring sequence B isdelayed relative to the sampling time T_(sa) for measuring sequence A bya duration (e.g., 10 ms) smaller than the pulse duration.

In some embodiments, data generated from each measuring sequence insupport of the center of mass method can also be used to estimatedistance using the ratio of mass method. The first measuring sequence Afrom the example illustrated in FIG. 13B is defined as T_(sa)=0, T₀=20ns, and can therefore measure in a range from 0 to 3 meters using theratio of mass method. If results of this first sequence A is combinedwith results of the second sequence B in which the sample time T_(sb)=10ns (half or approximately half of the pulse duration) with the samepulse duration of T₀=20 ns, the following distance ranges can beestimated:

Sequence A alone (ratio of mass): 0 m to 3 meters

Sequences A and B together (center of mass): 1.5 to 3 meters

Sequence B alone (ratio of mass): 1.5 to 4.5 meters

In some embodiments, different pulse widths and gating times can be usedwhen combining multiple sequences. In some scenarios, multiple sequencescan allow the total required sensing range to be satisfied whileachieving the precision of a shorter range defined by the pulse widthT₀.

Since the illumination signal and the received pulse energy decreaseover distance (mostly as the square of the distance), the further awaythe target is, the less signal is received by the photo detector. As thetotal range is divided into multiple subranges associated with differentmeasuring sequences, each measuring sequence can have different timingconfigurations and different numbers of integration pulses. In general,the received signal level (which gives rise to the value accumulated inthe measuring capacitor) should be increased for a subrange that is farfrom the sensor. The timing characteristics of the measuring sequencecan be tuned to the specific need of the subrange as follows in order tooptimize the total sensing time and the total energy required to meetthe performance goals:

Shorter pulse duration for ranges further away

Higher energy pulses for ranges further away

Larger number of pulses for ranges further away.

FIG. 11C is a timing diagram illustrating three measuringsequences—sequence A, sequence B, and sequence C—whereby each sequencehas a different pulse width (T_(0a), T_(0b), and T_(0e)), pulseamplitude, and number of pulses. The total measuring range is the sum ofthe three pulse widths T_(0a)+T_(0b)+T_(0e). The number of pulses foreach sequence, the amplitudes, and the durations of the pulses are afunction of the total range to be achieved as well as the level ofillumination irradiance over the distance from the sensor. The numbersof pulses, amplitudes, and pulse durations can be defined to achieve theperformance and precision goals of the sensor device. In the exampleillustrated in FIG. 11C, the second measuring sequence (sequence B) usesa pulse width T_(0b) of approximately half the width T_(0a) of the pulseemitted in the first sequence. Moreover, the sampling time T_(sb) usedin sequence B is delayed relative to sampling time T_(sa) of sequence Aby approximately the first pulse duration T_(0a). Similarly, the thirdmeasuring sequence (sequence C) uses a pulse width T_(0c) that isapproximately half the width T0 b of the pulse emitted in sequence B,and sampling time T_(sc) is delayed by a duration of approximately thesum of the first pulse duration T_(0a) and the second pulse durationT_(0b).

As in previous examples, according to some embodiments, each sequence A,B, and C may emit multiple pulses and capture the leading and trailingedge portions using the same control signal timings in order toaccumulate measurable amounts of electrical energy proportional to theleading and trailing edge portions of the pulse. Propagation times canbe calculated for each sequence based on this data, and the results canbe aggregated to obtain an aggregated propagation time. In somescenarios, an object may reside at a location within the range of one ofthe three sequences—e.g., sequence A—but outside the ranges of the othertwo sequences. In such scenarios, the distance determination component208 may identify the object based on the result of measuring sequence Awhile detecting no object in the results sequences B and C, andconsequently use the sequence A propagation time for the distancecalculation. For embodiments in which there is overlap between adjacentranges, an object may reside at a distance corresponding to an overlaprange between two consecutive sequences (e.g., sequences A and B). Ifdistance determination component 208 detects the object in the resultsof two consecutive sequences, the propagation times obtained from theresults of the two sequences may be aggregated (e.g., by averaging thetwo propagation times), and the aggregate propagation time can be usedfor the distance calculation.

Embodiments of TOF sensor device 202 described herein can measure thetime of flight of transmitted light pulses (and corresponding distancesof objects) with high accuracy while maintaining low acquisition andresponse times. This is achieved using techniques that generate largeamounts of information about a received pulse (and, in some embodiments,ambient light) quickly using relatively short measuring sequences. Thetime of flight estimation techniques described herein are also capableof compensating for, or rendering irrelevant, ambient light incident onthe sensor's photo-detectors. Some embodiments can achieve thesebenefits even in cases of irregular, non-rectangular light pulses.

FIGS. 21-23 illustrate various methodologies in accordance with one ormore embodiments of the subject application. While, for purposes ofsimplicity of explanation, the one or more methodologies shown hereinare shown and described as a series of acts, it is to be understood andappreciated that the subject innovation is not limited by the order ofacts, as some acts may, in accordance therewith, occur in a differentorder and/or concurrently with other acts from that shown and describedherein. For example, those skilled in the art will understand andappreciate that a methodology could alternatively be represented as aseries of interrelated states or events, such as in a state diagram.Moreover, not all illustrated acts may be required to implement amethodology in accordance with the innovation. Furthermore, interactiondiagram(s) may represent methodologies, or methods, in accordance withthe subject disclosure when disparate entities enact disparate portionsof the methodologies. Further yet, two or more of the disclosed examplemethods can be implemented in combination with each other, to accomplishone or more features or advantages described herein.

FIG. 19 illustrates an example methodology 1900 for determining adistance of an object or surface corresponding to a pixel of a TOFsensor image. Methodology 1900 may be suitable for execution on a TOFsensor device having an array of single-capacitor photo-detectors asillustrated in FIG. 3. Initially, at 1902, a light pulse is emitted intothe viewing space by a TOF sensor device. At 1904, at a time definedrelative to emission of the light pulse, a control signal is set thatcauses electrical charge generated by a photo-detector in proportioninto received light to be transferred to a measuring capacitor of theTOF sensor device. At 1906, an amount of electrical energy (e.g., acharge or voltage level) stored on the measuring capacitor is measuredafter receipt of a reflected light pulse corresponding to the emittedpulse at the photo-detector.

At 1908, a propagation time, or time of flight, of the emitted pulse iscalculated based on a determined fraction of the total received pulsethat is represented by the amount of electrical energy measured at step1906. This amount of electrical energy is proportional to the trailingportion of the reflected pulse received after the time that the controlsignal was set at step 1904, and is a function of the total propagationtime of the emitted light pulse. At 1910, a distance of an object orsurface from the TOF sensor device is calculated based on thepropagation time calculated at step 1908. This distance can bedetermined, for example, using equation (1) with the propagation timeentered as the time t. At 1912, a sensor output of the TOF sensor iscontrolled based on the distance determined at step 1910. For example,the TOF sensor device may be a component of an industrial safetyapplication that monitors a hazardous industrial area, and the sensoroutput may be an analog or digital output that controls a safety deviceor signals that power is to be removed from one or more hazardousmachines if the distance satisfies a defined criterion.

FIGS. 20A-20C illustrate an example methodology for determining adistance of an object or surface corresponding to a pixel of a TOFsensor image. This methodology, which calculates the distance using aratio method, may be suitable for execution on a TOF sensor devicehaving an array of three-capacitor photo-detectors as illustrated inFIGS. 8 and 10. The first part 2000A of the methodology is illustratedin FIG. 20A. Initially, at 2002, a first control signal that causeselectrical charge generated by a photo-detector in proportion toreceived light to be transferred to a first measuring capacitor of a TOFsensor device is set. At 2004, the first control signal is reset after adefined duration. At 2006, a determination is made as to whether Nmeasuring cycles are complete, where N is an integration factor of theTOF sensor device, and each measuring cycle comprises execution of steps2002 and 2004. If N measuring cycles have not yet been completed (NO atstep 2006), the methodology returns to step 2002, and steps 2002 and2004 are repeated until N measuring cycles have been completed. Theamount of electrical energy stored in the first measuring capacitorrepresents a measured amount of ambient light incident on the TOF sensordevice's photo-detector.

If N measuring cycles have been completed (YES at step 2006), themethodology proceeds to the second part 2000B illustrated in FIG. 20B.At 2008, another light pulse is emitted into the viewing space by theTOF sensor device. At 2010, at a first time defined relative to emissionof the light pulse at step 2008, a second control signal is set thatcauses the electrical charge generated by the photo-detector to betransferred to a second measuring capacitor. At 2012, at a second timedefined relative to the emission of the light pulse at step 2008, thesecond control signal is reset and a third control signal is set thatcauses the electrical charge generated by the photo-detector to betransferred to a third measuring capacitor. The second time, or samplingtime, is selected such that the duration during which the second controlsignal was set is equal (or approximately equal) to the defined durationof the first control signal. At 2014, the third control signal is resetafter receipt of a reflected pulse corresponding to the pulse emitted atstep 2008. The third control signal is reset after another definedduration equal to (or approximately equal to) the defined durations ofthe first and second control signals. The amounts of electrical energystored on the second and third measuring capacitors are proportional tothe leading and trailing portions, respectively, of the received lightpulse, where the respective portions are a function of the totalpropagation time of the light pulse.

At 2016, a determination is made as to whether N measuring cycles havebeen completed, where each measuring cycle comprises execution of steps2008-2014. If N measuring cycles have not been completed (NO at step2016), the methodology returns to step 2008, and steps 2008-2014 arerepeated. If N measuring cycles have been completed (YES at step 2016),the methodology proceeds to the second part 2000C illustrated in FIG.20C.

At step 2018, a first voltage VA stored on the first measuringcapacitor, a second voltage V1 stored on the second measuring capacitor,and a third voltage V2 stored on the third capacitor are measured.Voltage VA is proportional to the amount of ambient light incident onthe photo-detector, voltage V1 is proportional to the leading portion ofthe reflected pulse received while the second control signal was set,and voltage V2 is proportional to the trailing portion of the reflectedpulse received while the third control signal was set. In someembodiments, the voltage levels VA, V1, and V2 can be measured from therespective measuring capacitors as analog voltages (e.g., by one or moreamplifiers) and converted to digital values by one or more ADCs. At2020, a propagation time for the emitted light pulse is calculated basedon the measured values of VA, V1, and V2. For example, the propagationtime tp can be determined by the TOF sensor device's distancedetermination component based on any of equations (15), (16), or (17)discussed above. In general, the value of the propagation time tp can bedetermined by subtracting the ambient light voltage VA from both V1 andV2 to yield voltages proportional to the leading and trailing edges,respectively, of the received pulse, determining the ratio of thetrailing edge voltage to the total of the leading and trailing edgevoltages, and multiplying this ratio by the total time duration T₀ ofthe received light pulse. The voltages VA, V1, and V2 can be multipliedby capacitance mismatch compensation factors prior to this calculationto ensure accuracy, where the compensation factors can be obtained via acalibration sequence executed by the TOF sensor device.

At 2022, a distance d of an object or surface from the TOF sensor deviceis calculated based on the propagation time calculated at step 2020(e.g., using equation (1)). At 2024, a sensor output is controlled basedon the distance calculated at step 2022.

FIGS. 21A-21D illustrate an example methodology for determining adistance of an object or surface corresponding to a pixel of a TOFsensor image. This methodology, which calculates the distance using acenter of mass method, may be suitable for execution on a TOF sensordevice having an array of two-capacitor photo-detectors as illustratedin FIG. 6.

The first part 2100A of the methodology is illustrated in FIG. 21A. Thefirst part 2100A of the methodology represents a first of two measuringsequences to be carried out by the TOF sensor device. Initially, at2102, a first control signal is set that causes electrical chargegenerated by a photo-detector in proportion to received light to betransferred to a first measuring capacitor. At 2104, a light pulse isemitted into a viewing space by the TOF sensor device at a first timedefined relative to the start of the first control signal.

At 2106, at a sampling time defined relative to the start of the firstcontrol signal, the first control signal is reset and a second controlsignal is set that causes the electrical charge generated by thephoto-detector to be transferred to a second measuring capacitor. At2108, the second control signal is reset after receipt of a reflectedpulse corresponding to the pulse emitted at step 2104. The timings ofthe first and second control signals are such that the durations of bothcontrol signals are equal or approximately equal.

At 2110, a determination is made as to whether N measuring cycles havebeen completed, where N is the integration factor of the TOF sensordevice and each measuring cycle comprises execution of steps 2102-2108.If N measuring cycles have not yet been completed (NO at step 2110), themethodology returns to step 2102, and steps 2102-2108 are repeated foranother measuring cycle. If N measuring cycles have been completed (YESat step 2110), the methodology proceeds to the second part 2100Billustrated in FIG. 21B.

At 2112, a first voltage V_(C1a) stored on the first measuring capacitoris measured. This voltage V_(C1a) is proportional to the leading portionof the received pulse (and any ambient light) for the first measuringsequence. At 2114, a second voltage V_(C2a) stored on the secondmeasuring capacitor is measured. This voltage V_(C2a) is proportional tothe trailing portion of the received pulse (and any ambient light) forthe first measuring sequence. At 2116, the electrical charges stored onthe first and second measuring capacitors are cleared. The methodologythen moves to the third part 2100C illustrated in FIG. 21C.

The third part 2100C of the methodology represents the second measuringsequence carried out by the TOF sensor device. At 2118, the firstcontrol signal is set again to cause the electrical charge generated bythe photo-detector to be transferred to the first measuring capacitor.At 2120, another light pulse is emitted into the viewing space at asecond time defined relative to the start of the first control signal atstep 2118. The second time is delayed within the second sequence by aduration T₁ relative to the first time of the emission of the firstpulse within the first measuring sequence at step 2104. At 2122, at asampling time defined relative to the start of the first control signalat step 2118, the first control signal is reset and the second controlsignal is set to cause the electrical charge generated by thephoto-detector to be transferred to the second measuring capacitor. At2124, the second control signal is reset after receipt of a reflectedpulse corresponding to the emitted pulse. As in the first measuringsequence, the duration of the first and second control signals are equalor approximately equal.

At 2126, a determination is made as to whether N measuring cycles havebeen completed, where each measuring cycle comprises execution of steps2118-2124. If N measuring cycles have not yet been completed (NO at step2126), the methodology returns to step 2118, and steps 2118-2124 arerepeated for another measuring cycle. If N measuring cycles have beencompleted (YES at step 2126), the methodology proceeds to the fourthpart 2100D of the methodology illustrated in FIG. 21D.

At 2128, a first voltage V1 b stored on the first measuring capacitor ismeasured. This voltage V_(C1b) is proportional to the leading portion ofthe received pulse (and any ambient light) for the first measuringsequence. At 2130, a second voltage V_(C2b) stored on the secondmeasuring capacitor is measured. This voltage V_(C2b) is proportional tothe trailing portion of the received pulse (and any ambient light) forthe second measuring sequence. At 2132, the electrical charges stored onthe first and second measuring capacitors are cleared.

At 2134, a propagation time for the emitted pulses is calculated basedon the time delay T1 and the measured values of V_(C1a), V_(C1b),V_(C2a), and V_(C2b). For example, the TOF sensor device can calculatethe propagation time tp based equation (30) or (34). At 2136, a distanced of an object or surface from the TOF sensor device is calculated basedon the propagation time determined at step 2134 (e.g., using equation(1)). At 2138, a sensor output of the TOF sensor device is controlledbased on the distance value determined at step 2136.

Embodiments, systems, and components described herein, as well ascontrol systems and automation environments in which various aspects setforth in the subject specification can be carried out, can includecomputer or network components such as servers, clients, programmablelogic controllers (PLCs), automation controllers, communicationsmodules, mobile computers, on-board computers for mobile vehicles,wireless components, control components and so forth which are capableof interacting across a network. Computers and servers include one ormore processors—electronic integrated circuits that perform logicoperations employing electric signals—configured to execute instructionsstored in media such as random access memory (RAM), read only memory(ROM), a hard drives, as well as removable memory devices, which caninclude memory sticks, memory cards, flash drives, external hard drives,and so on.

Similarly, the term PLC or automation controller as used herein caninclude functionality that can be shared across multiple components,systems, and/or networks. As an example, one or more PLCs or automationcontrollers can communicate and cooperate with various network devicesacross the network. This can include substantially any type of control,communications module, computer, Input/Output (I/O) device, sensor,actuator, and human machine interface (HMI) that communicate via thenetwork, which includes control, automation, and/or public networks. ThePLC or automation controller can also communicate to and control variousother devices such as standard or safety-rated I/O modules includinganalog, digital, programmed/intelligent I/O modules, other programmablecontrollers, communications modules, sensors, actuators, output devices,and the like.

The network can include public networks such as the internet, intranets,and automation networks such as control and information protocol (CIP)networks including DeviceNet, ControlNet, safety networks, andEthernet/IP. Other networks include Ethernet, DH/DH+, Remote I/O,Fieldbus, Modbus, Profibus, CAN, wireless networks, serial protocols,and so forth. In addition, the network devices can include variouspossibilities (hardware and/or software components). These includecomponents such as switches with virtual local area network (VLAN)capability, LANs, WANs, proxies, gateways, routers, firewalls, virtualprivate network (VPN) devices, servers, clients, computers,configuration tools, monitoring tools, and/or other devices.

In order to provide a context for the various aspects of the disclosedsubject matter, FIGS. 22 and 23 as well as the following discussion areintended to provide a brief, general description of a suitableenvironment in which the various aspects of the disclosed subject mattermay be implemented.

With reference to FIG. 22, an example environment 2210 for implementingvarious aspects of the aforementioned subject matter includes a computer2212. The computer 2212 includes a processing unit 2214, a system memory2216, and a system bus 2218. The system bus 2218 couples systemcomponents including, but not limited to, the system memory 2216 to theprocessing unit 2214. The processing unit 2214 can be any of variousavailable processors. Multi-core microprocessors and othermultiprocessor architectures also can be employed as the processing unit2214.

The system bus 2218 can be any of several types of bus structure(s)including the memory bus or memory controller, a peripheral bus orexternal bus, and/or a local bus using any variety of available busarchitectures including, but not limited to, 8-bit bus, IndustrialStandard Architecture (ISA), Micro-Channel Architecture (MSA), ExtendedISA (EISA), Intelligent Drive Electronics (IDE), VESA Local Bus (VLB),Peripheral Component Interconnect (PCI), Universal Serial Bus (USB),Advanced Graphics Port (AGP), Personal Computer Memory CardInternational Association bus (PCMCIA), and Small Computer SystemsInterface (SCSI).

The system memory 2216 includes volatile memory 2220 and nonvolatilememory 2222. The basic input/output system (BIOS), containing the basicroutines to transfer information between elements within the computer2212, such as during start-up, is stored in nonvolatile memory 2222. Byway of illustration, and not limitation, nonvolatile memory 2222 caninclude read only memory (ROM), programmable ROM (PROM), electricallyprogrammable ROM (EPROM), electrically erasable PROM (EEPROM), or flashmemory. Volatile memory 2220 includes random access memory (RAM), whichacts as external cache memory. By way of illustration and notlimitation, RAM is available in many forms such as synchronous RAM(SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rateSDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), anddirect Rambus RAM (DRRAM).

Computer 2212 also includes removable/non-removable,volatile/non-volatile computer storage media. FIG. 22 illustrates, forexample a disk storage 2224. Disk storage 2224 includes, but is notlimited to, devices like a magnetic disk drive, floppy disk drive, tapedrive, Jaz drive, Zip drive, LS-100 drive, flash memory card, or memorystick. In addition, disk storage 2224 can include storage mediaseparately or in combination with other storage media including, but notlimited to, an optical disk drive such as a compact disk ROM device(CD-ROM), CD recordable drive (CD-R Drive), CD rewritable drive (CD-RWDrive) or a digital versatile disk ROM drive (DVD-ROM). To facilitateconnection of the disk storage 2224 to the system bus 2218, a removableor non-removable interface is typically used such as interface 2226.

It is to be appreciated that FIG. 22 describes software that acts as anintermediary between users and the basic computer resources described insuitable operating environment 2210. Such software includes an operatingsystem 2228. Operating system 2228, which can be stored on disk storage2224, acts to control and allocate resources of the computer 2212.System applications 2230 take advantage of the management of resourcesby operating system 2228 through program modules 2232 and program data2234 stored either in system memory 2216 or on disk storage 2224. It isto be appreciated that one or more embodiments of the subject disclosurecan be implemented with various operating systems or combinations ofoperating systems.

A user enters commands or information into the computer 2212 throughinput device(s) 2236. Input devices 2236 include, but are not limitedto, a pointing device such as a mouse, trackball, stylus, touch pad,keyboard, microphone, joystick, game pad, satellite dish, scanner, TVtuner card, digital camera, digital video camera, web camera, and thelike. These and other input devices connect to the processing unit 2214through the system bus 2218 via interface port(s) 2238. Interfaceport(s) 2238 include, for example, a serial port, a parallel port, agame port, and a universal serial bus (USB). Output device(s) 2240 usesome of the same type of ports as input device(s) 2236. Thus, forexample, a USB port may be used to provide input to computer 2212, andto output information from computer 2212 to an output device 2240.Output adapters 2242 are provided to illustrate that there are someoutput devices 2240 like monitors, speakers, and printers, among otheroutput devices 2240, which require special adapters. The output adapters2242 include, by way of illustration and not limitation, video and soundcards that provide a means of connection between the output device 2240and the system bus 2218. It should be noted that other devices and/orsystems of devices provide both input and output capabilities such asremote computer(s) 2244.

Computer 2212 can operate in a networked environment using logicalconnections to one or more remote computers, such as remote computer(s)2244. The remote computer(s) 2244 can be a personal computer, a server,a router, a network PC, a workstation, a microprocessor based appliance,a peer device or other common network node and the like, and typicallyincludes many or all of the elements described relative to computer2212. For purposes of brevity, only a memory storage device 2246 isillustrated with remote computer(s) 2244. Remote computer(s) 2244 islogically connected to computer 2212 through a network interface 2248and then physically connected via communication connection 2250. Networkinterface 2248 encompasses communication networks such as local-areanetworks (LAN) and wide-area networks (WAN). LAN technologies includeFiber Distributed Data Interface (FDDI), Copper Distributed DataInterface (CDDI), Ethernet/IEEE 802.3, Token Ring/IEEE 802.5 and thelike. WAN technologies include, but are not limited to, point-to-pointlinks, circuit switching networks like Integrated Services DigitalNetworks (ISDN) and variations thereon, packet switching networks, andDigital Subscriber Lines (DSL).

Communication connection(s) 2250 refers to the hardware/softwareemployed to connect the network interface 2248 to the system bus 2218.While communication connection 2250 is shown for illustrative clarityinside computer 2212, it can also be external to computer 2212. Thehardware/software necessary for connection to the network interface 2248includes, for exemplary purposes only, internal and externaltechnologies such as, modems including regular telephone grade modems,cable modems and DSL modems, ISDN adapters, and Ethernet cards.

FIG. 23 is a schematic block diagram of a sample computing environment2300 with which the disclosed subject matter can interact. The samplecomputing environment 2300 includes one or more client(s) 2302. Theclient(s) 2302 can be hardware and/or software (e.g., threads,processes, computing devices). The sample computing environment 2300also includes one or more server(s) 2304. The server(s) 2304 can also behardware and/or software (e.g., threads, processes, computing devices).The servers 2304 can house threads to perform transformations byemploying one or more embodiments as described herein, for example. Onepossible communication between a client 2302 and servers 2304 can be inthe form of a data packet adapted to be transmitted between two or morecomputer processes. The sample computing environment 2300 includes acommunication framework 2306 that can be employed to facilitatecommunications between the client(s) 2302 and the server(s) 2304. Theclient(s) 2302 are operably connected to one or more client datastore(s) 2308 that can be employed to store information local to theclient(s) 2302. Similarly, the server(s) 2304 are operably connected toone or more server data store(s) 2310 that can be employed to storeinformation local to the servers 2304.

What has been described above includes examples of the subjectinnovation. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe disclosed subject matter, but one of ordinary skill in the art mayrecognize that many further combinations and permutations of the subjectinnovation are possible. Accordingly, the disclosed subject matter isintended to embrace all such alterations, modifications, and variationsthat fall within the spirit and scope of the appended claims.

In particular and in regard to the various functions performed by theabove described components, devices, circuits, systems and the like, theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., a functional equivalent), even though not structurallyequivalent to the disclosed structure, which performs the function inthe herein illustrated exemplary aspects of the disclosed subjectmatter. In this regard, it will also be recognized that the disclosedsubject matter includes a system as well as a computer-readable mediumhaving computer-executable instructions for performing the acts and/orevents of the various methods of the disclosed subject matter.

In addition, while a particular feature of the disclosed subject mattermay have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular application. Furthermore, to the extent thatthe terms “includes,” and “including” and variants thereof are used ineither the detailed description or the claims, these terms are intendedto be inclusive in a manner similar to the term “comprising.”

In this application, the word “exemplary” is used to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Rather, use of the wordexemplary is intended to present concepts in a concrete fashion.

Various aspects or features described herein may be implemented as amethod, apparatus, or article of manufacture using standard programmingand/or engineering techniques. The term “article of manufacture” as usedherein is intended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. For example, computerreadable media can include but are not limited to magnetic storagedevices (e.g., hard disk, floppy disk, magnetic strips . . . ), opticaldisks [e.g., compact disk (CD), digital versatile disk (DVD) . . . ],smart cards, and flash memory devices (e.g., card, stick, key drive . .. ).

What is claimed is:
 1. A time of flight sensor device, comprising: anemitter component configured to emit a light pulse at a first timeduring a measuring sequence; a photo-sensor component comprising aphoto-detector, the photo-detector comprising a photo device configuredto generate electrical energy in proportion to a quantity of receivedlight, a first measuring capacitor connected to the photo device via afirst control line switch, a second measuring capacitor connected to thephoto device via a second control line switch, and a third measuringcapacitor connected to the photo device via a third control line switch,wherein the photo-sensor component is configured to set a first controlsignal of the first control line switch at a second time during themeasuring sequence defined relative to the first time, and reset thefirst control signal at a third time, wherein setting the first controlsignal at the second time and resetting the first control signal at thethird time causes a first portion of the electrical energy proportionalto a leading portion of a received reflected light pulse correspondingto the light pulse emitted by the emitter component to be stored in thefirst measuring capacitor, and set a second control signal of the secondcontrol line switch at the third time, wherein setting the secondcontrol signal at the third time causes a second portion of theelectrical energy proportional to a trailing portion of the receivedreflected pulse to be stored in the second measuring capacitor; and adistance determination component configured to determine a propagationtime for the light pulse based on a first measured value of the firstportion of the electrical energy, a second measured value of the secondportion of the electrical energy, and a third measured value of a thirdportion of the electrical energy corresponding to ambient light storedon the third measuring capacitor.
 2. The time of flight sensor device ofclaim 1, wherein the distance determination component is configured todetermine the propagation time based on a ratio of the second measuredvalue to a total of the first measured value and the second measuredvalue.
 3. The time of flight sensor device of claim 1, wherein thephoto-sensor component is further configured to, while the receivedreflected light pulse is not being received at the photo-detector, set athird control signal of the third control line switch for a durationequal to or substantially equal to a first duration of the first controlsignal and a second duration of the second control signal, whereinsetting the third control signal for the duration causes the thirdportion of the electrical energy to be stored on the third measuringcapacitor, and the distance determination component is furtherconfigured to subtract the third measured value of the third portion ofthe electrical energy from the first measured value and the secondmeasured value to yield a leading pulse portion value and a trailingpulse portion value, respectively, and to determine the propagation timebased on a ratio of the trailing pulse portion value to a total of theleading pulse portion value and the trailing pulse portion value.
 4. Thetime of flight sensor device of claim 3, wherein the distancedetermination component is configured to determine the propagation timebased on$t_{p} = {{\frac{{\alpha \; V\; 2} - {\beta \; V_{A}}}{{{V\; 1} +} \propto {{V\; 2} - {2\; \beta \; V_{a}}}}T_{0}} + T_{S}}$where tp is the propagation time, T₀ is a duration of the receivedreflected light pulse, V1 is the first measured value, V2 is the secondmeasured value, V_(A) is the third measured value, β is a firstcompensation factor based on a mismatch between the third measuringcapacitor and the first measuring capacitor, and α is a secondcompensation factor based on a capacitance mismatch between the firstmeasuring capacitor and the second measuring capacitor.
 5. The time offlight sensor device of claim 4, wherein the light pulse is a firstlight pulse, the received reflected light pulse is a first receivedreflected light pulse, the emitter component is further configured toemit a second light pulse at a fourth time during a first part of acalibration sequence and a third light pulse at a fifth time during asecond part of the calibration sequence, the photo-sensor component isfurther configured to: during the first part of the calibrationsequence: set the first control signal at a sixth time defined relativeto the fourth time, and reset the first control signal at a seventhtime, wherein setting the first control signal at the sixth time andresetting the first control signal at the seventh time causes a fourthportion of the electrical energy proportional to a leading portion of asecond received reflected light pulse corresponding to the second lightpulse to be stored in the first measuring capacitor, and set the secondcontrol signal at the seventh time, wherein setting the second controlsignal at the seventh time causes a fifth portion of the electricalenergy proportional to a trailing portion of the second receivedreflected pulse to be stored in the second measuring capacitor, measureand store the fourth portion as a fourth measured value V1 a, andmeasure and store the fifth portion as a fifth measured value V2 a, andduring the second part of the calibration sequence: set the firstcontrol signal at an eighth time defined relative to the fifth time, andreset the first control signal at a ninth time, wherein setting thefirst control signal at the eighth time and resetting the first controlsignal at the ninth time causes a sixth portion of the electrical energyproportional to a leading portion of a third received reflected lightpulse corresponding to the third light pulse to be stored in the firstmeasuring capacitor, and set the second control signal at the ninthtime, wherein setting the second control signal at the ninth time causesa seventh portion of the electrical energy proportional to a trailingportion of the third received reflected pulse to be stored in the secondmeasuring capacitor, measure and store the sixth portion as a sixthmeasured value V1 b, and measure and store the seventh portion as aseventh measured value V2 b, and the distance determination component isconfigured to set the second compensation factor α based on the fourthmeasured value V1 a, the fifth measured value V2 a, the sixth measuredvalue V1 b, and the seventh measured value V2 b.
 6. The time of flightsensor of claim 5, wherein the distance determination component isconfigured to set the second compensation factor α according to:$\propto {= {\frac{{V\; 1\; a} - {V\; 1\; b}}{{V\; 2\; b} - {V\; 2\; a}}.}}$7. The time of flight sensor device of claim 2, wherein the measuringsequence is a first measuring sequence of a measuring cycle, the lightpulse is a first light pulse, the received reflected light pulse is afirst received reflected light pulse, the emitter component isconfigured to emit a second light pulse at a fourth time during a secondmeasuring sequence of the measuring cycle, the second light pulse havinga same pulse duration as the first light pulse, and the photo-sensorcomponent is configured to set the first control signal at a fifth timedefined relative to the fourth time and reset the first control signalat a sixth time, subsequent to the fifth time, defined relative to thefourth time, wherein a first duration between a falling edge of thesecond light pulse and the sixth time exceeds a second duration betweena falling edge of the first light pulse and the third time by a delayapproximately equal to the pulse duration, and wherein setting the firstcontrol signal at the fifth time and resetting the first control signalat the sixth time causes a fourth portion of the electrical energyproportional to a leading portion of a second received reflected lightpulse corresponding to the second light pulse to be stored in the firstmeasuring capacitor, and set the second control signal at the sixthtime, wherein setting the second control signal at the sixth time causesa fifth portion of the electrical energy proportional to a trailingportion of the second received reflected pulse to be stored in thesecond measuring capacitor, and the distance determination component isfurther configured to determine the propagation time further based on afourth measured value of the fourth portion of the electrical energy,and a fifth measured value of the fifth portion of the electricalenergy.
 8. The time of flight sensor device of claim 2, wherein themeasuring sequence is a first measuring sequence of a measuring cycle,the light pulse is a first light pulse having a first pulse duration,the received reflected light pulse is a first received reflected lightpulse, the emitter component is configured to emit a second light pulseat a fourth time during a second measuring sequence of the measuringcycle, the second light pulse having a second pulse duration that isapproximately half of the first pulse duration, and the photo-sensorcomponent is configured to set the first control signal at a fifth timedefined relative to the fourth time and reset the first control signalat a sixth time, subsequent to the fifth time, defined relative to thefourth time, wherein a first duration between a falling edge of thesecond light pulse and the sixth time exceeds a second duration betweena falling edge of the first light pulse and the third time by a delayapproximately equal to the pulse duration, and wherein setting the firstcontrol signal at the fifth time and resetting the first control signalat the sixth time causes a fourth portion of the electrical energyproportional to a leading portion of a second received reflected lightpulse corresponding to the second light pulse to be stored in the firstmeasuring capacitor, and set the second control signal at the sixthtime, wherein setting the second control signal at the sixth time causesa fifth portion of the electrical energy proportional to a trailingportion of the second received reflected pulse to be stored in thesecond measuring capacitor, and the distance determination component isfurther configured to determine the propagation time further based on afourth measured value of the fourth portion of the electrical energy anda fifth measured value of the fifth portion of the electrical energy. 9.The time of flight sensor device of claim 1, wherein the distancedetermination component is further configured to determine, based on thepropagation time, a distance of an object or a surface corresponding toa pixel that corresponds to the photo-detector, and the time of flightsensor device further comprises a control output component configured togenerate an output signal in response to determining that the distancesatisfies a defined criterion.
 10. A method for measuring a distance ofan object, comprising: generating, by a photo device of a photo-detectorof a time of flight sensor device comprising a processor, electricalenergy in proportion to a quantity of light received at the photodevice; emitting, by the time of flight sensor device, a light pulse ata first time within a measuring sequence; setting, by the time of flightsensor device at a second time during the measuring sequence definedrelative to the first time, a first control signal of a first controlline switch; resetting, by the time of flight sensor device at a thirdtime, the first control signal, wherein the setting the first controlsignal at the second time and the resetting the first control signal atthe third time causes a first portion of the electrical energyproportional to a leading portion of a received reflected light pulsecorresponding to the light pulse to be stored in a first measuringcapacitor connected to the photo device via the first control lineswitch; setting, by the time of flight sensor device at the third time,a second control signal of a second control line switch, wherein thesetting the second control signal at the third time causes a secondportion of the electrical energy proportional to a trailing portion ofthe received reflected pulse to be stored in a second measuringcapacitor connected to the photo device via the second control lineswitch; and determining, by the time of flight sensor device, apropagation time for the light pulse based on a first measured value ofthe first portion of the electrical energy, a second measured value ofthe second portion of the electrical energy, and a third measured valueof a third portion of the electrical energy corresponding to ambientlight stored on a third measuring capacitor.
 11. The method of claim 10,wherein the determining comprises determining the propagation time basedon a ratio of the second measured value to a total of the first measuredvalue and the second measured value.
 12. The method of claim 10, furthercomprising: during a period in which the received reflected light pulseis not being received at the photo-detector, setting, by the time offlight sensor device, a third control signal of a third control lineswitch for a duration equal to or substantially equal to a firstduration of the first control signal and a second duration of the secondcontrol signal, wherein the setting the third control signal for theduration causes the third portion of the electrical energy to be storedon the third measuring capacitor, wherein the determining comprisessubtracting the third measured value from the first measured value toyield a leading pulse portion value subtracting the third measured valuefrom the second measured value to yield a trailing pulse portion value,and determining the propagation time based on a ratio of the trailingpulse portion value to a total of the leading pulse portion value andthe trailing pulse portion value.
 13. The method of claim 12, whereinthe determining the propagation time comprises determining thepropagation time based on$t_{p} = {{\frac{{\alpha \; V\; 2} - {\beta \; V_{A}}}{{{V\; 1} +} \propto {{V\; 2} - {2\; \beta \; V_{A}}}}T_{0}} + T_{S}}$where tp is the propagation time, T₀ is a duration of the receivedreflected light pulse, V1 is the first measured value, V2 is the secondmeasured value, V_(A) is the third measured value, β is a firstcompensation factor based on a mismatch between the third measuringcapacitor and the first measuring capacitor, and α is a secondcompensation factor based on a capacitance mismatch between the firstmeasuring capacitor and the second measuring capacitor.
 14. The methodof claim 13, wherein the light pulse is a first light pulse, and thereceived reflected light pulse is a first received reflected lightpulse, and the method further comprises: during a first part of acalibration sequence: emitting, by the time of flight sensor device, asecond light pulse at a fourth time; setting, by the time of flightsensor device, the first control signal at a fifth time defined relativeto the fourth time, resetting, by the time of flight sensor device, thefirst control signal at a sixth time, wherein the setting the firstcontrol signal at the fifth time and the resetting the first controlsignal at the sixth time causes a fourth portion of the electricalenergy proportional to a leading portion of a second received reflectedlight pulse corresponding to the second light pulse to be stored in thefirst measuring capacitor; setting, by the time of flight sensor device,the second control signal at the sixth time, wherein the setting thesecond control signal at the sixth time causes a fifth portion of theelectrical energy proportional to a trailing portion of the secondreceived reflected pulse to be stored in the second measuring capacitor;measuring and storing, by the time of flight sensor device, the fourthportion as a fourth measured value V1 a; and measuring and storing, bythe time of flight sensor device, the fifth portion as a fifth measuredvalue V2 a; and during a second part of the calibration sequence:emitting, by the time of flight sensor device, a third light pulse at aneighth time; setting, by the time of flight sensor device, the firstcontrol signal at a ninth time defined relative to the eighth time;resetting, by the time of flight sensor device, the first control signalat a tenth time, wherein the setting the first control signal at theninth time and the resetting the first control signal at the tenth timecauses a sixth portion of the electrical energy proportional to aleading portion of a third received reflected light pulse correspondingto the third light pulse to be stored in the first measuring capacitor;setting, by the time of flight sensor device, the second control signalat the tenth time, wherein the setting the second control signal at thetenth time causes a seventh portion of the electrical energyproportional to a trailing portion of the third received reflected pulseto be stored in the second measuring capacitor; measuring and storing,by the time of flight sensor device, the sixth portion as a sixthmeasured value V1 b, and measuring and storing, by the time of flightsensor device, the seventh portion as a seventh measured value V2 b; andsetting, by the time of flight sensor device, the second compensationfactor α based on the fourth measured value V1 a, the fifth measuredvalue V2 a, the sixth measured value V1 b, and the seventh measuredvalue V2 b.
 15. The method of claim 14, wherein the setting the secondcompensation factor α comprises setting the second compensation factor αaccording to:$\propto {= {\frac{{V\; 1\; a} - {V\; 1\; b}}{{V\; 2\; b} - {V\; 2\; a}}.}}$16. The method of claim 11, wherein the measuring sequence is a firstmeasuring sequence of a measuring cycle, the light pulse is a firstlight pulse, and the received reflected light pulse is a first receivedreflected light pulse, and the method further comprises: emitting, bythe time of flight sensor device, a second light pulse at a fourth timeduring a second measuring sequence of the measuring cycle, the secondlight pulse having a same pulse duration as the first light pulse;setting, by the time of flight sensor device, the first control signalat a fifth time defined relative to the fourth time; resetting, by thetime of flight sensor device, the first control signal at a sixth time,subsequent to the fifth time, defined relative to the fourth time,wherein a first duration between a falling edge of the second lightpulse and the sixth time exceeds a second duration between a fallingedge of the first light pulse and the third time by a delayapproximately equal to the pulse duration, and wherein the setting thefirst control signal at the fifth time and the resetting the firstcontrol signal at the sixth time causes a fourth portion of theelectrical energy proportional to a leading portion of a second receivedreflected light pulse corresponding to the second light pulse to bestored in the first measuring capacitor; and setting, by the time offlight sensor device, the second control signal at the sixth time,wherein the setting the second control signal at the sixth time causes afifth portion of the electrical energy proportional to a trailingportion of the second received reflected pulse to be stored in thesecond measuring capacitor, wherein the determining the propagation timecomprises determining the propagation time further based on a fourthmeasured value of the fourth portion of the electrical energy, and afifth measured value of the fifth portion of the electrical energy. 17.The method of claim 11, wherein the measuring sequence is a firstmeasuring sequence of a measuring cycle, the light pulse is a firstlight pulse having a first pulse duration, the received reflected lightpulse is a first received reflected light pulse, and the method furthercomprises: emitting, by the time of flight sensor device, a second lightpulse at a fourth time during a second measuring sequence of themeasuring cycle, the second light pulse having a second pulse durationthat is approximately half of the first pulse duration; setting, by thetime of flight sensor device, the first control signal at a fifth timedefined relative to the fourth time; resetting, by the time of flightsensor device, the first control signal at a sixth time, subsequent tothe fifth time, defined relative to the fourth time, wherein a firstduration between a falling edge of the second light pulse and the sixthtime exceeds a second duration between a falling edge of the first lightpulse and the third time by a delay approximately equal to the pulseduration, and wherein the setting the first control signal at the fifthtime and the resetting the first control signal at the sixth time causesa fourth portion of the electrical energy proportional to a leadingportion of a second received reflected light pulse corresponding to thesecond light pulse to be stored in the first measuring capacitor; andsetting, by the time of flight sensor device, the second control signalat the sixth time, wherein the setting the second control signal at thesixth time causes a fifth portion of the electrical energy proportionalto a trailing portion of the second received reflected pulse to bestored in the second measuring capacitor, wherein the determining thepropagation time comprises determining the propagation time furtherbased on a fourth measured value of the fourth portion of the electricalenergy and a fifth measured value of the fifth portion of the electricalenergy.
 18. The method of claim 10, further comprising: determining, bythe time of flight sensor device based on the propagation time, adistance of an object or a surface corresponding to a pixel thatcorresponds to the photo-detector; and in response to determining thatthe distance satisfies a defined criterion, generating, by the time offlight sensor device, an output signal.
 19. A non-transitorycomputer-readable medium having stored thereon instructions that, inresponse to execution, cause a time of flight sensor device comprising aprocessor and a photo device that generates electrical energy inproportion to a quantity of received light, to perform operations, theoperations comprising: initiating emission of a light pulse at a firsttime within a measuring sequence; setting, at a second time during themeasuring sequence defined relative to the first time, a first controlsignal of a first control line switch; resetting, at a third time, thefirst control signal, wherein the setting the first control signal atthe second time and the resetting the first control signal at the thirdtime causes a first portion of the electrical energy proportional to aleading portion of a received reflected light pulse corresponding to thelight pulse to be stored in a first measuring capacitor connected to thephoto device via the first control line switch; setting, at the thirdtime, a second control signal of a second control line switch, whereinthe setting the second control signal at the third time causes a secondportion of the electrical energy proportional to a trailing portion ofthe received reflected pulse to be stored in a second measuringcapacitor connected to the photo device via the second control lineswitch; and determining a propagation time for the light pulse based ona first measured value of the first portion of the electrical energy, asecond measured value of the second portion of the electrical energy,and a third measured value of a third portion of the electrical energycorresponding to ambient light stored on a third measuring capacitor.20. The non-transitory computer-readable medium of claim 19, wherein thedetermining comprises determining the propagation time based on a ratioof the second measured value to a total of the first measured value andthe second measured value.